r4639 - in glibc-doc-reference: tags tags/2.13-1/debian tags/2.13-1/manual trunk/manual
Author: aurel32
Date: 2011-05-02 18:20:00 +0000 (Mon, 02 May 2011)
New Revision: 4639
Added:
glibc-doc-reference/tags/2.13-1/
glibc-doc-reference/tags/2.13-1/debian/README.source
glibc-doc-reference/tags/2.13-1/debian/changelog
glibc-doc-reference/tags/2.13-1/debian/control
glibc-doc-reference/tags/2.13-1/manual/.gitignore
glibc-doc-reference/tags/2.13-1/manual/charset.texi
glibc-doc-reference/tags/2.13-1/manual/pkgvers.texi
glibc-doc-reference/tags/2.13-1/manual/texis
glibc-doc-reference/trunk/manual/.gitignore
glibc-doc-reference/trunk/manual/texis
Removed:
glibc-doc-reference/tags/2.13-1/debian/README.source
glibc-doc-reference/tags/2.13-1/debian/changelog
glibc-doc-reference/tags/2.13-1/debian/control
glibc-doc-reference/tags/2.13-1/manual/.cvsignore
glibc-doc-reference/tags/2.13-1/manual/charset.texi
glibc-doc-reference/tags/2.13-1/manual/linuxthreads.texi
glibc-doc-reference/trunk/manual/.cvsignore
glibc-doc-reference/trunk/manual/linuxthreads.texi
Modified:
glibc-doc-reference/tags/2.13-1/manual/Makefile
glibc-doc-reference/tags/2.13-1/manual/arith.texi
glibc-doc-reference/tags/2.13-1/manual/errno.texi
glibc-doc-reference/tags/2.13-1/manual/getopt.texi
glibc-doc-reference/tags/2.13-1/manual/install.texi
glibc-doc-reference/tags/2.13-1/manual/libc.texinfo
glibc-doc-reference/tags/2.13-1/manual/locale.texi
glibc-doc-reference/tags/2.13-1/manual/math.texi
glibc-doc-reference/tags/2.13-1/manual/memory.texi
glibc-doc-reference/tags/2.13-1/manual/message.texi
glibc-doc-reference/tags/2.13-1/manual/resource.texi
glibc-doc-reference/tags/2.13-1/manual/stdio.texi
glibc-doc-reference/tags/2.13-1/manual/time.texi
glibc-doc-reference/trunk/manual/Makefile
glibc-doc-reference/trunk/manual/arith.texi
glibc-doc-reference/trunk/manual/charset.texi
glibc-doc-reference/trunk/manual/errno.texi
glibc-doc-reference/trunk/manual/getopt.texi
glibc-doc-reference/trunk/manual/install.texi
glibc-doc-reference/trunk/manual/libc.texinfo
glibc-doc-reference/trunk/manual/locale.texi
glibc-doc-reference/trunk/manual/math.texi
glibc-doc-reference/trunk/manual/memory.texi
glibc-doc-reference/trunk/manual/message.texi
glibc-doc-reference/trunk/manual/resource.texi
glibc-doc-reference/trunk/manual/stdio.texi
glibc-doc-reference/trunk/manual/time.texi
Log:
Tag glibc-doc-reference 2.13-1
Deleted: glibc-doc-reference/tags/2.13-1/debian/README.source
===================================================================
--- glibc-doc-reference/trunk/debian/README.source 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/debian/README.source 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,6 +0,0 @@
-glibc-doc-reference_<version>.orig.tar.gz contains the glibc-<version>/manual
-directory of upstream http://ftp.gnu.org/gnu/glibc/glibc-<version>.tar.bz2
-It has been created with the following commands:
- bzip2 -c -d glibc-2.6.1.tar.bz2 |\
- tarcust -x 'glibc-2.6.1/(?!manual).*' |\
- gzip -9 > glibc-doc-reference_2.6.1.orig.tar.gz
Copied: glibc-doc-reference/tags/2.13-1/debian/README.source (from rev 4638, glibc-doc-reference/trunk/debian/README.source)
===================================================================
--- glibc-doc-reference/tags/2.13-1/debian/README.source (rev 0)
+++ glibc-doc-reference/tags/2.13-1/debian/README.source 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,6 @@
+glibc-doc-reference_<version>.orig.tar.gz contains the glibc-<version>/manual
+directory of upstream http://ftp.gnu.org/gnu/glibc/glibc-<version>.tar.bz2
+It has been created with the following commands:
+ bzip2 -c -d glibc-2.13.tar.bz2 |\
+ tarcust -x 'glibc-2.131/(?!manual).*' |\
+ gzip -9 > glibc-doc-reference_2.13.orig.tar.gz
Deleted: glibc-doc-reference/tags/2.13-1/debian/changelog
===================================================================
--- glibc-doc-reference/trunk/debian/changelog 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/debian/changelog 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,87 +0,0 @@
-glibc-doc-reference (2.9-3) UNRELEASED; urgency=low
-
- * Remove Ben Collins <bcollins@debian.org> from the uploaders (Closes:
- bug#540903).
-
- -- Aurelien Jarno <aurel32@debian.org> Tue, 11 Aug 2009 00:07:30 +0200
-
-glibc-doc-reference (2.9-2) unstable; urgency=low
-
- * Add patch from Sven Joachim to prevent indexing every libc
- function (closes: bug#536506).
- * Bump Standards-Version to 3.8.2.
- * Switch to debhelper 5.0.
-
- -- Aurelien Jarno <aurel32@debian.org> Sat, 11 Jul 2009 13:04:34 +0200
-
-glibc-doc-reference (2.9-1) unstable; urgency=low
-
- * New upstream version.
- * Update debian/copyright.
- * Fix error reported by lintian in glibc-doc-reference.doc-base.
- * Bump Standards-Version to 3.8.0.
-
- -- Aurelien Jarno <aurel32@debian.org> Mon, 23 Feb 2009 02:55:42 +0100
-
-glibc-doc-reference (2.7-1) unstable; urgency=low
-
- * New upstream version.
- * Update texinfo.tex (closes: bug#452256).
- * Also build the PDF manual.
-
- -- Aurelien Jarno <aurel32@debian.org> Tue, 27 Nov 2007 01:16:50 +0100
-
-glibc-doc-reference (2.6.1-1) unstable; urgency=low
-
- * New upstream version.
-
- -- Aurelien Jarno <aurel32@debian.org> Wed, 01 Aug 2007 07:45:17 +0200
-
-glibc-doc-reference (2.6-2) unstable; urgency=low
-
- * Upload to unstable.
-
- -- Aurelien Jarno <aurel32@debian.org> Tue, 10 Jul 2007 09:31:24 +0200
-
-glibc-doc-reference (2.6-1) experimental; urgency=low
-
- * New upstream version.
- * Add linuxthreads documentation (closes: bug#426558).
-
- -- Aurelien Jarno <aurel32@debian.org> Wed, 30 May 2007 15:21:37 +0200
-
-glibc-doc-reference (2.5-2) unstable; urgency=low
-
- * Upload to unstable (closes: bug#418893).
-
- -- Aurelien Jarno <aurel32@debian.org> Thu, 12 Apr 2007 18:09:05 +0200
-
-glibc-doc-reference (2.5-1) experimental; urgency=low
-
- * New upstream version.
-
- -- Aurelien Jarno <aurel32@debian.org> Sun, 1 Oct 2006 19:30:46 +0200
-
-glibc-doc-reference (2.3.999-3) experimental; urgency=low
-
- * debian/copyright: update FSF address.
- * debian/control:
- - move debhelper to Build-Depends (from Build-Depends-Indep).
- - bumped Standards-Version to 3.7.2 (no changes).
-
- -- Aurelien Jarno <aurel32@debian.org> Tue, 15 Aug 2006 21:05:29 +0200
-
-glibc-doc-reference (2.3.999-2) experimental; urgency=low
-
- * The source package needs to go into non-free too, thanks Joerg Jaspert.
-
- -- Denis Barbier <barbier@debian.org> Sun, 26 Mar 2006 22:44:49 +0200
-
-glibc-doc-reference (2.3.999-1) experimental; urgency=low
-
- * For licensing reasons, the GNU C Library Reference Manual cannot be
- distributed in Debian and has to be shipped in the non-free section.
- * This release is shipped in experimental, its version number will be
- set to 2.4 and uploaded to unstable along with glibc 2.4.
-
- -- Denis Barbier <barbier@debian.org> Fri, 24 Mar 2006 23:49:03 +0100
Copied: glibc-doc-reference/tags/2.13-1/debian/changelog (from rev 4638, glibc-doc-reference/trunk/debian/changelog)
===================================================================
--- glibc-doc-reference/tags/2.13-1/debian/changelog (rev 0)
+++ glibc-doc-reference/tags/2.13-1/debian/changelog 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,111 @@
+glibc-doc-reference (2.13-1) unstable; urgency=low
+
+ * New upstream version:
+ - Fix rpmatch() example wrt getline() usage (closes: #367849).
+ * Bump Standards-Version to 3.9.2.
+
+ -- Aurelien Jarno <aurel32@debian.org> Mon, 02 May 2011 19:39:48 +0200
+
+glibc-doc-reference (2.11.1-2) unstable; urgency=low
+
+ * Build depends on texlive-latex-base (closes: #611411).
+
+ -- Aurelien Jarno <aurel32@debian.org> Sat, 29 Jan 2011 19:32:10 +0100
+
+glibc-doc-reference (2.11.1-1) unstable; urgency=low
+
+ * New usptream version.
+ * Bump Standards-Version to 3.8.4.
+
+ -- Aurelien Jarno <aurel32@debian.org> Tue, 08 Jun 2010 16:53:14 +0200
+
+glibc-doc-reference (2.10.1-1) unstable; urgency=low
+
+ * New upstream version.
+ * Bump Standards-Version to 3.8.3.
+ * Rebuild against recent debhelper (closes: bug#550897).
+ * Remove Ben Collins <bcollins@debian.org> from the uploaders (Closes:
+ bug#540903).
+
+ -- Aurelien Jarno <aurel32@debian.org> Sun, 18 Oct 2009 20:24:25 +0000
+
+glibc-doc-reference (2.9-2) unstable; urgency=low
+
+ * Add patch from Sven Joachim to prevent indexing every libc
+ function (closes: bug#536506).
+ * Bump Standards-Version to 3.8.2.
+ * Switch to debhelper 5.0.
+
+ -- Aurelien Jarno <aurel32@debian.org> Sat, 11 Jul 2009 13:04:34 +0200
+
+glibc-doc-reference (2.9-1) unstable; urgency=low
+
+ * New upstream version.
+ * Update debian/copyright.
+ * Fix error reported by lintian in glibc-doc-reference.doc-base.
+ * Bump Standards-Version to 3.8.0.
+
+ -- Aurelien Jarno <aurel32@debian.org> Mon, 23 Feb 2009 02:55:42 +0100
+
+glibc-doc-reference (2.7-1) unstable; urgency=low
+
+ * New upstream version.
+ * Update texinfo.tex (closes: bug#452256).
+ * Also build the PDF manual.
+
+ -- Aurelien Jarno <aurel32@debian.org> Tue, 27 Nov 2007 01:16:50 +0100
+
+glibc-doc-reference (2.6.1-1) unstable; urgency=low
+
+ * New upstream version.
+
+ -- Aurelien Jarno <aurel32@debian.org> Wed, 01 Aug 2007 07:45:17 +0200
+
+glibc-doc-reference (2.6-2) unstable; urgency=low
+
+ * Upload to unstable.
+
+ -- Aurelien Jarno <aurel32@debian.org> Tue, 10 Jul 2007 09:31:24 +0200
+
+glibc-doc-reference (2.6-1) experimental; urgency=low
+
+ * New upstream version.
+ * Add linuxthreads documentation (closes: bug#426558).
+
+ -- Aurelien Jarno <aurel32@debian.org> Wed, 30 May 2007 15:21:37 +0200
+
+glibc-doc-reference (2.5-2) unstable; urgency=low
+
+ * Upload to unstable (closes: bug#418893).
+
+ -- Aurelien Jarno <aurel32@debian.org> Thu, 12 Apr 2007 18:09:05 +0200
+
+glibc-doc-reference (2.5-1) experimental; urgency=low
+
+ * New upstream version.
+
+ -- Aurelien Jarno <aurel32@debian.org> Sun, 1 Oct 2006 19:30:46 +0200
+
+glibc-doc-reference (2.3.999-3) experimental; urgency=low
+
+ * debian/copyright: update FSF address.
+ * debian/control:
+ - move debhelper to Build-Depends (from Build-Depends-Indep).
+ - bumped Standards-Version to 3.7.2 (no changes).
+
+ -- Aurelien Jarno <aurel32@debian.org> Tue, 15 Aug 2006 21:05:29 +0200
+
+glibc-doc-reference (2.3.999-2) experimental; urgency=low
+
+ * The source package needs to go into non-free too, thanks Joerg Jaspert.
+
+ -- Denis Barbier <barbier@debian.org> Sun, 26 Mar 2006 22:44:49 +0200
+
+glibc-doc-reference (2.3.999-1) experimental; urgency=low
+
+ * For licensing reasons, the GNU C Library Reference Manual cannot be
+ distributed in Debian and has to be shipped in the non-free section.
+ * This release is shipped in experimental, its version number will be
+ set to 2.4 and uploaded to unstable along with glibc 2.4.
+
+ -- Denis Barbier <barbier@debian.org> Fri, 24 Mar 2006 23:49:03 +0100
Deleted: glibc-doc-reference/tags/2.13-1/debian/control
===================================================================
--- glibc-doc-reference/trunk/debian/control 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/debian/control 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,16 +0,0 @@
-Source: glibc-doc-reference
-Section: non-free/doc
-Priority: optional
-Build-Depends: debhelper (>= 5.0.0)
-Build-Depends-Indep: texinfo, texi2html, gawk, texlive-base-bin
-Maintainer: GNU Libc Maintainers <debian-glibc@lists.debian.org>
-Uploaders: GOTO Masanori <gotom@debian.org>, Philip Blundell <pb@nexus.co.uk>, Jeff Bailey <jbailey@raspberryginger.com>, Daniel Jacobowitz <dan@debian.org>, Clint Adams <schizo@debian.org>, Aurelien Jarno <aurel32@debian.org>
-Standards-Version: 3.8.2
-
-Package: glibc-doc-reference
-Architecture: all
-Section: non-free/doc
-Priority: optional
-Conflicts: glibc-doc (<< 2.4)
-Description: GNU C Library: Documentation
- Contains The GNU C Library Reference manual in info, pdf and html format.
Copied: glibc-doc-reference/tags/2.13-1/debian/control (from rev 4638, glibc-doc-reference/trunk/debian/control)
===================================================================
--- glibc-doc-reference/tags/2.13-1/debian/control (rev 0)
+++ glibc-doc-reference/tags/2.13-1/debian/control 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,17 @@
+Source: glibc-doc-reference
+Section: non-free/doc
+Priority: optional
+Build-Depends: debhelper (>= 5.0.0)
+Build-Depends-Indep: texinfo, texi2html, gawk, texlive-base-bin, texlive-latex-base
+Maintainer: GNU Libc Maintainers <debian-glibc@lists.debian.org>
+Uploaders: GOTO Masanori <gotom@debian.org>, Jeff Bailey <jbailey@raspberryginger.com>, Daniel Jacobowitz <dan@debian.org>, Clint Adams <schizo@debian.org>, Aurelien Jarno <aurel32@debian.org>
+Standards-Version: 3.9.2
+
+Package: glibc-doc-reference
+Architecture: all
+Section: non-free/doc
+Priority: optional
+Depends: ${misc:Depends}
+Conflicts: glibc-doc (<< 2.4)
+Description: GNU C Library: Documentation
+ Contains The GNU C Library Reference manual in info, pdf and html format.
Deleted: glibc-doc-reference/tags/2.13-1/manual/.cvsignore
===================================================================
--- glibc-doc-reference/trunk/manual/.cvsignore 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/.cvsignore 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,14 +0,0 @@
-*.d *.o *.so *.po *.go stamp.* *.stamp *.ustamp *.udeps
-*.gz *.Z *.tar *.tgz *.bz2
-=*
-TODO COPYING* AUTHORS copyr-* copying.*
-glibc-*
-
-*.dvi* *.info* *.c.texi *.ps *.pdf
-*.toc *.aux *.log *.tmp
-*.cp *.cps *.fn *.fns *.vr *.vrs *.tp *.tps *.ky *.kys *.pg *.pgs
-
-texis top-menu.texi chapters.texi summary.texi stamp-*
-distinfo dir-add.texinfo dir-add.texi
-
-libm-err.texi
Added: glibc-doc-reference/tags/2.13-1/manual/.gitignore
===================================================================
--- glibc-doc-reference/tags/2.13-1/manual/.gitignore (rev 0)
+++ glibc-doc-reference/tags/2.13-1/manual/.gitignore 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,29 @@
+*.aux
+*.c.texi
+*.cp
+*.cps
+*.dvi*
+*.fn
+*.fns
+*.info*
+*.ky
+*.kys
+*.log
+*.pdf
+*.pg
+*.pgs
+*.ps
+*.tmp
+*.toc
+*.tp
+*.tps
+*.vr
+*.vrs
+chapters.texi
+dir-add.texi
+dir-add.texinfo
+libm-err.texi
+stamp-*
+summary.texi
+texis
+top-menu.texi
Modified: glibc-doc-reference/tags/2.13-1/manual/Makefile
===================================================================
--- glibc-doc-reference/trunk/manual/Makefile 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/Makefile 2011-05-02 18:20:00 UTC (rev 4639)
@@ -58,7 +58,7 @@
pipe socket terminal syslog math arith time \
resource setjmp signal startup process job nss \
users sysinfo conf crypt debug)
-add-chapters = linuxthreads.texi
+add-chapters = $(wildcard $(foreach d, $(add-ons), ../$d/$d.texi))
appendices = lang.texi header.texi install.texi maint.texi contrib.texi \
freemanuals.texi
@@ -232,9 +232,12 @@
.PHONY: stubs
stubs: $(objpfx)stubs
endif
-$(objpfx)stubs ../po/manual.pot $(objpfx)stamp%:
+$(objpfx)stubs ../po/manual.pot:
$(make-target-directory)
touch $@
+$(objpfx)stamp%:
+ $(make-target-directory)
+ touch $@
# Make the target directory if it doesn't exist, using the `mkinstalldirs'
# script that does `mkdir -p' even if `mkdir' doesn't support that flag.
Modified: glibc-doc-reference/tags/2.13-1/manual/arith.texi
===================================================================
--- glibc-doc-reference/trunk/manual/arith.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/arith.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1407,7 +1407,8 @@
@comment ISO
@deftypefunx {long double} roundl (long double @var{x})
These functions are similar to @code{rint}, but they round halfway
-cases away from zero instead of to the nearest even integer.
+cases away from zero instead of to the nearest integer (or other
+current rounding mode).
@end deftypefun
@comment math.h
Deleted: glibc-doc-reference/tags/2.13-1/manual/charset.texi
===================================================================
--- glibc-doc-reference/trunk/manual/charset.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/charset.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,2895 +0,0 @@
-@node Character Set Handling, Locales, String and Array Utilities, Top
-@c %MENU% Support for extended character sets
-@chapter Character Set Handling
-
-@ifnottex
-@macro cal{text}
-\text\
-@end macro
-@end ifnottex
-
-Character sets used in the early days of computing had only six, seven,
-or eight bits for each character: there was never a case where more than
-eight bits (one byte) were used to represent a single character. The
-limitations of this approach became more apparent as more people
-grappled with non-Roman character sets, where not all the characters
-that make up a language's character set can be represented by @math{2^8}
-choices. This chapter shows the functionality that was added to the C
-library to support multiple character sets.
-
-@menu
-* Extended Char Intro:: Introduction to Extended Characters.
-* Charset Function Overview:: Overview about Character Handling
- Functions.
-* Restartable multibyte conversion:: Restartable multibyte conversion
- Functions.
-* Non-reentrant Conversion:: Non-reentrant Conversion Function.
-* Generic Charset Conversion:: Generic Charset Conversion.
-@end menu
-
-
-@node Extended Char Intro
-@section Introduction to Extended Characters
-
-A variety of solutions is available to overcome the differences between
-character sets with a 1:1 relation between bytes and characters and
-character sets with ratios of 2:1 or 4:1. The remainder of this
-section gives a few examples to help understand the design decisions
-made while developing the functionality of the @w{C library}.
-
-@cindex internal representation
-A distinction we have to make right away is between internal and
-external representation. @dfn{Internal representation} means the
-representation used by a program while keeping the text in memory.
-External representations are used when text is stored or transmitted
-through some communication channel. Examples of external
-representations include files waiting in a directory to be
-read and parsed.
-
-Traditionally there has been no difference between the two representations.
-It was equally comfortable and useful to use the same single-byte
-representation internally and externally. This comfort level decreases
-with more and larger character sets.
-
-One of the problems to overcome with the internal representation is
-handling text that is externally encoded using different character
-sets. Assume a program that reads two texts and compares them using
-some metric. The comparison can be usefully done only if the texts are
-internally kept in a common format.
-
-@cindex wide character
-For such a common format (@math{=} character set) eight bits are certainly
-no longer enough. So the smallest entity will have to grow: @dfn{wide
-characters} will now be used. Instead of one byte per character, two or
-four will be used instead. (Three are not good to address in memory and
-more than four bytes seem not to be necessary).
-
-@cindex Unicode
-@cindex ISO 10646
-As shown in some other part of this manual,
-@c !!! Ahem, wide char string functions are not yet covered -- drepper
-a completely new family has been created of functions that can handle wide
-character texts in memory. The most commonly used character sets for such
-internal wide character representations are Unicode and @w{ISO 10646}
-(also known as UCS for Universal Character Set). Unicode was originally
-planned as a 16-bit character set; whereas, @w{ISO 10646} was designed to
-be a 31-bit large code space. The two standards are practically identical.
-They have the same character repertoire and code table, but Unicode specifies
-added semantics. At the moment, only characters in the first @code{0x10000}
-code positions (the so-called Basic Multilingual Plane, BMP) have been
-assigned, but the assignment of more specialized characters outside this
-16-bit space is already in progress. A number of encodings have been
-defined for Unicode and @w{ISO 10646} characters:
-@cindex UCS-2
-@cindex UCS-4
-@cindex UTF-8
-@cindex UTF-16
-UCS-2 is a 16-bit word that can only represent characters
-from the BMP, UCS-4 is a 32-bit word than can represent any Unicode
-and @w{ISO 10646} character, UTF-8 is an ASCII compatible encoding where
-ASCII characters are represented by ASCII bytes and non-ASCII characters
-by sequences of 2-6 non-ASCII bytes, and finally UTF-16 is an extension
-of UCS-2 in which pairs of certain UCS-2 words can be used to encode
-non-BMP characters up to @code{0x10ffff}.
-
-To represent wide characters the @code{char} type is not suitable. For
-this reason the @w{ISO C} standard introduces a new type that is
-designed to keep one character of a wide character string. To maintain
-the similarity there is also a type corresponding to @code{int} for
-those functions that take a single wide character.
-
-@comment stddef.h
-@comment ISO
-@deftp {Data type} wchar_t
-This data type is used as the base type for wide character strings.
-In other words, arrays of objects of this type are the equivalent of
-@code{char[]} for multibyte character strings. The type is defined in
-@file{stddef.h}.
-
-The @w{ISO C90} standard, where @code{wchar_t} was introduced, does not
-say anything specific about the representation. It only requires that
-this type is capable of storing all elements of the basic character set.
-Therefore it would be legitimate to define @code{wchar_t} as @code{char},
-which might make sense for embedded systems.
-
-But for GNU systems @code{wchar_t} is always 32 bits wide and, therefore,
-capable of representing all UCS-4 values and, therefore, covering all of
-@w{ISO 10646}. Some Unix systems define @code{wchar_t} as a 16-bit type
-and thereby follow Unicode very strictly. This definition is perfectly
-fine with the standard, but it also means that to represent all
-characters from Unicode and @w{ISO 10646} one has to use UTF-16 surrogate
-characters, which is in fact a multi-wide-character encoding. But
-resorting to multi-wide-character encoding contradicts the purpose of the
-@code{wchar_t} type.
-@end deftp
-
-@comment wchar.h
-@comment ISO
-@deftp {Data type} wint_t
-@code{wint_t} is a data type used for parameters and variables that
-contain a single wide character. As the name suggests this type is the
-equivalent of @code{int} when using the normal @code{char} strings. The
-types @code{wchar_t} and @code{wint_t} often have the same
-representation if their size is 32 bits wide but if @code{wchar_t} is
-defined as @code{char} the type @code{wint_t} must be defined as
-@code{int} due to the parameter promotion.
-
-@pindex wchar.h
-This type is defined in @file{wchar.h} and was introduced in
-@w{Amendment 1} to @w{ISO C90}.
-@end deftp
-
-As there are for the @code{char} data type macros are available for
-specifying the minimum and maximum value representable in an object of
-type @code{wchar_t}.
-
-@comment wchar.h
-@comment ISO
-@deftypevr Macro wint_t WCHAR_MIN
-The macro @code{WCHAR_MIN} evaluates to the minimum value representable
-by an object of type @code{wint_t}.
-
-This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
-@end deftypevr
-
-@comment wchar.h
-@comment ISO
-@deftypevr Macro wint_t WCHAR_MAX
-The macro @code{WCHAR_MAX} evaluates to the maximum value representable
-by an object of type @code{wint_t}.
-
-This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
-@end deftypevr
-
-Another special wide character value is the equivalent to @code{EOF}.
-
-@comment wchar.h
-@comment ISO
-@deftypevr Macro wint_t WEOF
-The macro @code{WEOF} evaluates to a constant expression of type
-@code{wint_t} whose value is different from any member of the extended
-character set.
-
-@code{WEOF} need not be the same value as @code{EOF} and unlike
-@code{EOF} it also need @emph{not} be negative. In other words, sloppy
-code like
-
-@smallexample
-@{
- int c;
- @dots{}
- while ((c = getc (fp)) < 0)
- @dots{}
-@}
-@end smallexample
-
-@noindent
-has to be rewritten to use @code{WEOF} explicitly when wide characters
-are used:
-
-@smallexample
-@{
- wint_t c;
- @dots{}
- while ((c = wgetc (fp)) != WEOF)
- @dots{}
-@}
-@end smallexample
-
-@pindex wchar.h
-This macro was introduced in @w{Amendment 1} to @w{ISO C90} and is
-defined in @file{wchar.h}.
-@end deftypevr
-
-
-These internal representations present problems when it comes to storing
-and transmittal. Because each single wide character consists of more
-than one byte, they are effected by byte-ordering. Thus, machines with
-different endianesses would see different values when accessing the same
-data. This byte ordering concern also applies for communication protocols
-that are all byte-based and therefore require that the sender has to
-decide about splitting the wide character in bytes. A last (but not least
-important) point is that wide characters often require more storage space
-than a customized byte-oriented character set.
-
-@cindex multibyte character
-@cindex EBCDIC
-For all the above reasons, an external encoding that is different from
-the internal encoding is often used if the latter is UCS-2 or UCS-4.
-The external encoding is byte-based and can be chosen appropriately for
-the environment and for the texts to be handled. A variety of different
-character sets can be used for this external encoding (information that
-will not be exhaustively presented here--instead, a description of the
-major groups will suffice). All of the ASCII-based character sets
-fulfill one requirement: they are "filesystem safe." This means that
-the character @code{'/'} is used in the encoding @emph{only} to
-represent itself. Things are a bit different for character sets like
-EBCDIC (Extended Binary Coded Decimal Interchange Code, a character set
-family used by IBM), but if the operation system does not understand
-EBCDIC directly the parameters-to-system calls have to be converted
-first anyhow.
-
-@itemize @bullet
-@item
-The simplest character sets are single-byte character sets. There can
-be only up to 256 characters (for @w{8 bit} character sets), which is
-not sufficient to cover all languages but might be sufficient to handle
-a specific text. Handling of a @w{8 bit} character sets is simple. This
-is not true for other kinds presented later, and therefore, the
-application one uses might require the use of @w{8 bit} character sets.
-
-@cindex ISO 2022
-@item
-The @w{ISO 2022} standard defines a mechanism for extended character
-sets where one character @emph{can} be represented by more than one
-byte. This is achieved by associating a state with the text.
-Characters that can be used to change the state can be embedded in the
-text. Each byte in the text might have a different interpretation in each
-state. The state might even influence whether a given byte stands for a
-character on its own or whether it has to be combined with some more
-bytes.
-
-@cindex EUC
-@cindex Shift_JIS
-@cindex SJIS
-In most uses of @w{ISO 2022} the defined character sets do not allow
-state changes that cover more than the next character. This has the
-big advantage that whenever one can identify the beginning of the byte
-sequence of a character one can interpret a text correctly. Examples of
-character sets using this policy are the various EUC character sets
-(used by Sun's operations systems, EUC-JP, EUC-KR, EUC-TW, and EUC-CN)
-or Shift_JIS (SJIS, a Japanese encoding).
-
-But there are also character sets using a state that is valid for more
-than one character and has to be changed by another byte sequence.
-Examples for this are ISO-2022-JP, ISO-2022-KR, and ISO-2022-CN.
-
-@item
-@cindex ISO 6937
-Early attempts to fix 8 bit character sets for other languages using the
-Roman alphabet lead to character sets like @w{ISO 6937}. Here bytes
-representing characters like the acute accent do not produce output
-themselves: one has to combine them with other characters to get the
-desired result. For example, the byte sequence @code{0xc2 0x61}
-(non-spacing acute accent, followed by lower-case `a') to get the ``small
-a with acute'' character. To get the acute accent character on its own,
-one has to write @code{0xc2 0x20} (the non-spacing acute followed by a
-space).
-
-Character sets like @w{ISO 6937} are used in some embedded systems such
-as teletex.
-
-@item
-@cindex UTF-8
-Instead of converting the Unicode or @w{ISO 10646} text used internally,
-it is often also sufficient to simply use an encoding different than
-UCS-2/UCS-4. The Unicode and @w{ISO 10646} standards even specify such an
-encoding: UTF-8. This encoding is able to represent all of @w{ISO
-10646} 31 bits in a byte string of length one to six.
-
-@cindex UTF-7
-There were a few other attempts to encode @w{ISO 10646} such as UTF-7,
-but UTF-8 is today the only encoding that should be used. In fact, with
-any luck UTF-8 will soon be the only external encoding that has to be
-supported. It proves to be universally usable and its only disadvantage
-is that it favors Roman languages by making the byte string
-representation of other scripts (Cyrillic, Greek, Asian scripts) longer
-than necessary if using a specific character set for these scripts.
-Methods like the Unicode compression scheme can alleviate these
-problems.
-@end itemize
-
-The question remaining is: how to select the character set or encoding
-to use. The answer: you cannot decide about it yourself, it is decided
-by the developers of the system or the majority of the users. Since the
-goal is interoperability one has to use whatever the other people one
-works with use. If there are no constraints, the selection is based on
-the requirements the expected circle of users will have. In other words,
-if a project is expected to be used in only, say, Russia it is fine to use
-KOI8-R or a similar character set. But if at the same time people from,
-say, Greece are participating one should use a character set that allows
-all people to collaborate.
-
-The most widely useful solution seems to be: go with the most general
-character set, namely @w{ISO 10646}. Use UTF-8 as the external encoding
-and problems about users not being able to use their own language
-adequately are a thing of the past.
-
-One final comment about the choice of the wide character representation
-is necessary at this point. We have said above that the natural choice
-is using Unicode or @w{ISO 10646}. This is not required, but at least
-encouraged, by the @w{ISO C} standard. The standard defines at least a
-macro @code{__STDC_ISO_10646__} that is only defined on systems where
-the @code{wchar_t} type encodes @w{ISO 10646} characters. If this
-symbol is not defined one should avoid making assumptions about the wide
-character representation. If the programmer uses only the functions
-provided by the C library to handle wide character strings there should
-be no compatibility problems with other systems.
-
-@node Charset Function Overview
-@section Overview about Character Handling Functions
-
-A Unix @w{C library} contains three different sets of functions in two
-families to handle character set conversion. One of the function families
-(the most commonly used) is specified in the @w{ISO C90} standard and,
-therefore, is portable even beyond the Unix world. Unfortunately this
-family is the least useful one. These functions should be avoided
-whenever possible, especially when developing libraries (as opposed to
-applications).
-
-The second family of functions got introduced in the early Unix standards
-(XPG2) and is still part of the latest and greatest Unix standard:
-@w{Unix 98}. It is also the most powerful and useful set of functions.
-But we will start with the functions defined in @w{Amendment 1} to
-@w{ISO C90}.
-
-@node Restartable multibyte conversion
-@section Restartable Multibyte Conversion Functions
-
-The @w{ISO C} standard defines functions to convert strings from a
-multibyte representation to wide character strings. There are a number
-of peculiarities:
-
-@itemize @bullet
-@item
-The character set assumed for the multibyte encoding is not specified
-as an argument to the functions. Instead the character set specified by
-the @code{LC_CTYPE} category of the current locale is used; see
-@ref{Locale Categories}.
-
-@item
-The functions handling more than one character at a time require NUL
-terminated strings as the argument (i.e., converting blocks of text
-does not work unless one can add a NUL byte at an appropriate place).
-The GNU C library contains some extensions to the standard that allow
-specifying a size, but basically they also expect terminated strings.
-@end itemize
-
-Despite these limitations the @w{ISO C} functions can be used in many
-contexts. In graphical user interfaces, for instance, it is not
-uncommon to have functions that require text to be displayed in a wide
-character string if the text is not simple ASCII. The text itself might
-come from a file with translations and the user should decide about the
-current locale, which determines the translation and therefore also the
-external encoding used. In such a situation (and many others) the
-functions described here are perfect. If more freedom while performing
-the conversion is necessary take a look at the @code{iconv} functions
-(@pxref{Generic Charset Conversion}).
-
-@menu
-* Selecting the Conversion:: Selecting the conversion and its properties.
-* Keeping the state:: Representing the state of the conversion.
-* Converting a Character:: Converting Single Characters.
-* Converting Strings:: Converting Multibyte and Wide Character
- Strings.
-* Multibyte Conversion Example:: A Complete Multibyte Conversion Example.
-@end menu
-
-@node Selecting the Conversion
-@subsection Selecting the conversion and its properties
-
-We already said above that the currently selected locale for the
-@code{LC_CTYPE} category decides about the conversion that is performed
-by the functions we are about to describe. Each locale uses its own
-character set (given as an argument to @code{localedef}) and this is the
-one assumed as the external multibyte encoding. The wide character
-character set always is UCS-4, at least on GNU systems.
-
-A characteristic of each multibyte character set is the maximum number
-of bytes that can be necessary to represent one character. This
-information is quite important when writing code that uses the
-conversion functions (as shown in the examples below).
-The @w{ISO C} standard defines two macros that provide this information.
-
-
-@comment limits.h
-@comment ISO
-@deftypevr Macro int MB_LEN_MAX
-@code{MB_LEN_MAX} specifies the maximum number of bytes in the multibyte
-sequence for a single character in any of the supported locales. It is
-a compile-time constant and is defined in @file{limits.h}.
-@pindex limits.h
-@end deftypevr
-
-@comment stdlib.h
-@comment ISO
-@deftypevr Macro int MB_CUR_MAX
-@code{MB_CUR_MAX} expands into a positive integer expression that is the
-maximum number of bytes in a multibyte character in the current locale.
-The value is never greater than @code{MB_LEN_MAX}. Unlike
-@code{MB_LEN_MAX} this macro need not be a compile-time constant, and in
-the GNU C library it is not.
-
-@pindex stdlib.h
-@code{MB_CUR_MAX} is defined in @file{stdlib.h}.
-@end deftypevr
-
-Two different macros are necessary since strictly @w{ISO C90} compilers
-do not allow variable length array definitions, but still it is desirable
-to avoid dynamic allocation. This incomplete piece of code shows the
-problem:
-
-@smallexample
-@{
- char buf[MB_LEN_MAX];
- ssize_t len = 0;
-
- while (! feof (fp))
- @{
- fread (&buf[len], 1, MB_CUR_MAX - len, fp);
- /* @r{@dots{} process} buf */
- len -= used;
- @}
-@}
-@end smallexample
-
-The code in the inner loop is expected to have always enough bytes in
-the array @var{buf} to convert one multibyte character. The array
-@var{buf} has to be sized statically since many compilers do not allow a
-variable size. The @code{fread} call makes sure that @code{MB_CUR_MAX}
-bytes are always available in @var{buf}. Note that it isn't
-a problem if @code{MB_CUR_MAX} is not a compile-time constant.
-
-
-@node Keeping the state
-@subsection Representing the state of the conversion
-
-@cindex stateful
-In the introduction of this chapter it was said that certain character
-sets use a @dfn{stateful} encoding. That is, the encoded values depend
-in some way on the previous bytes in the text.
-
-Since the conversion functions allow converting a text in more than one
-step we must have a way to pass this information from one call of the
-functions to another.
-
-@comment wchar.h
-@comment ISO
-@deftp {Data type} mbstate_t
-@cindex shift state
-A variable of type @code{mbstate_t} can contain all the information
-about the @dfn{shift state} needed from one call to a conversion
-function to another.
-
-@pindex wchar.h
-@code{mbstate_t} is defined in @file{wchar.h}. It was introduced in
-@w{Amendment 1} to @w{ISO C90}.
-@end deftp
-
-To use objects of type @code{mbstate_t} the programmer has to define such
-objects (normally as local variables on the stack) and pass a pointer to
-the object to the conversion functions. This way the conversion function
-can update the object if the current multibyte character set is stateful.
-
-There is no specific function or initializer to put the state object in
-any specific state. The rules are that the object should always
-represent the initial state before the first use, and this is achieved by
-clearing the whole variable with code such as follows:
-
-@smallexample
-@{
- mbstate_t state;
- memset (&state, '\0', sizeof (state));
- /* @r{from now on @var{state} can be used.} */
- @dots{}
-@}
-@end smallexample
-
-When using the conversion functions to generate output it is often
-necessary to test whether the current state corresponds to the initial
-state. This is necessary, for example, to decide whether to emit
-escape sequences to set the state to the initial state at certain
-sequence points. Communication protocols often require this.
-
-@comment wchar.h
-@comment ISO
-@deftypefun int mbsinit (const mbstate_t *@var{ps})
-The @code{mbsinit} function determines whether the state object pointed
-to by @var{ps} is in the initial state. If @var{ps} is a null pointer or
-the object is in the initial state the return value is nonzero. Otherwise
-it is zero.
-
-@pindex wchar.h
-@code{mbsinit} was introduced in @w{Amendment 1} to @w{ISO C90} and is
-declared in @file{wchar.h}.
-@end deftypefun
-
-Code using @code{mbsinit} often looks similar to this:
-
-@c Fix the example to explicitly say how to generate the escape sequence
-@c to restore the initial state.
-@smallexample
-@{
- mbstate_t state;
- memset (&state, '\0', sizeof (state));
- /* @r{Use @var{state}.} */
- @dots{}
- if (! mbsinit (&state))
- @{
- /* @r{Emit code to return to initial state.} */
- const wchar_t empty[] = L"";
- const wchar_t *srcp = empty;
- wcsrtombs (outbuf, &srcp, outbuflen, &state);
- @}
- @dots{}
-@}
-@end smallexample
-
-The code to emit the escape sequence to get back to the initial state is
-interesting. The @code{wcsrtombs} function can be used to determine the
-necessary output code (@pxref{Converting Strings}). Please note that on
-GNU systems it is not necessary to perform this extra action for the
-conversion from multibyte text to wide character text since the wide
-character encoding is not stateful. But there is nothing mentioned in
-any standard that prohibits making @code{wchar_t} using a stateful
-encoding.
-
-@node Converting a Character
-@subsection Converting Single Characters
-
-The most fundamental of the conversion functions are those dealing with
-single characters. Please note that this does not always mean single
-bytes. But since there is very often a subset of the multibyte
-character set that consists of single byte sequences, there are
-functions to help with converting bytes. Frequently, ASCII is a subpart
-of the multibyte character set. In such a scenario, each ASCII character
-stands for itself, and all other characters have at least a first byte
-that is beyond the range @math{0} to @math{127}.
-
-@comment wchar.h
-@comment ISO
-@deftypefun wint_t btowc (int @var{c})
-The @code{btowc} function (``byte to wide character'') converts a valid
-single byte character @var{c} in the initial shift state into the wide
-character equivalent using the conversion rules from the currently
-selected locale of the @code{LC_CTYPE} category.
-
-If @code{(unsigned char) @var{c}} is no valid single byte multibyte
-character or if @var{c} is @code{EOF}, the function returns @code{WEOF}.
-
-Please note the restriction of @var{c} being tested for validity only in
-the initial shift state. No @code{mbstate_t} object is used from
-which the state information is taken, and the function also does not use
-any static state.
-
-@pindex wchar.h
-The @code{btowc} function was introduced in @w{Amendment 1} to @w{ISO C90}
-and is declared in @file{wchar.h}.
-@end deftypefun
-
-Despite the limitation that the single byte value always is interpreted
-in the initial state this function is actually useful most of the time.
-Most characters are either entirely single-byte character sets or they
-are extension to ASCII. But then it is possible to write code like this
-(not that this specific example is very useful):
-
-@smallexample
-wchar_t *
-itow (unsigned long int val)
-@{
- static wchar_t buf[30];
- wchar_t *wcp = &buf[29];
- *wcp = L'\0';
- while (val != 0)
- @{
- *--wcp = btowc ('0' + val % 10);
- val /= 10;
- @}
- if (wcp == &buf[29])
- *--wcp = L'0';
- return wcp;
-@}
-@end smallexample
-
-Why is it necessary to use such a complicated implementation and not
-simply cast @code{'0' + val % 10} to a wide character? The answer is
-that there is no guarantee that one can perform this kind of arithmetic
-on the character of the character set used for @code{wchar_t}
-representation. In other situations the bytes are not constant at
-compile time and so the compiler cannot do the work. In situations like
-this it is necessary @code{btowc}.
-
-@noindent
-There also is a function for the conversion in the other direction.
-
-@comment wchar.h
-@comment ISO
-@deftypefun int wctob (wint_t @var{c})
-The @code{wctob} function (``wide character to byte'') takes as the
-parameter a valid wide character. If the multibyte representation for
-this character in the initial state is exactly one byte long, the return
-value of this function is this character. Otherwise the return value is
-@code{EOF}.
-
-@pindex wchar.h
-@code{wctob} was introduced in @w{Amendment 1} to @w{ISO C90} and
-is declared in @file{wchar.h}.
-@end deftypefun
-
-There are more general functions to convert single character from
-multibyte representation to wide characters and vice versa. These
-functions pose no limit on the length of the multibyte representation
-and they also do not require it to be in the initial state.
-
-@comment wchar.h
-@comment ISO
-@deftypefun size_t mbrtowc (wchar_t *restrict @var{pwc}, const char *restrict @var{s}, size_t @var{n}, mbstate_t *restrict @var{ps})
-@cindex stateful
-The @code{mbrtowc} function (``multibyte restartable to wide
-character'') converts the next multibyte character in the string pointed
-to by @var{s} into a wide character and stores it in the wide character
-string pointed to by @var{pwc}. The conversion is performed according
-to the locale currently selected for the @code{LC_CTYPE} category. If
-the conversion for the character set used in the locale requires a state,
-the multibyte string is interpreted in the state represented by the
-object pointed to by @var{ps}. If @var{ps} is a null pointer, a static,
-internal state variable used only by the @code{mbrtowc} function is
-used.
-
-If the next multibyte character corresponds to the NUL wide character,
-the return value of the function is @math{0} and the state object is
-afterwards in the initial state. If the next @var{n} or fewer bytes
-form a correct multibyte character, the return value is the number of
-bytes starting from @var{s} that form the multibyte character. The
-conversion state is updated according to the bytes consumed in the
-conversion. In both cases the wide character (either the @code{L'\0'}
-or the one found in the conversion) is stored in the string pointed to
-by @var{pwc} if @var{pwc} is not null.
-
-If the first @var{n} bytes of the multibyte string possibly form a valid
-multibyte character but there are more than @var{n} bytes needed to
-complete it, the return value of the function is @code{(size_t) -2} and
-no value is stored. Please note that this can happen even if @var{n}
-has a value greater than or equal to @code{MB_CUR_MAX} since the input
-might contain redundant shift sequences.
-
-If the first @code{n} bytes of the multibyte string cannot possibly form
-a valid multibyte character, no value is stored, the global variable
-@code{errno} is set to the value @code{EILSEQ}, and the function returns
-@code{(size_t) -1}. The conversion state is afterwards undefined.
-
-@pindex wchar.h
-@code{mbrtowc} was introduced in @w{Amendment 1} to @w{ISO C90} and
-is declared in @file{wchar.h}.
-@end deftypefun
-
-Use of @code{mbrtowc} is straightforward. A function that copies a
-multibyte string into a wide character string while at the same time
-converting all lowercase characters into uppercase could look like this
-(this is not the final version, just an example; it has no error
-checking, and sometimes leaks memory):
-
-@smallexample
-wchar_t *
-mbstouwcs (const char *s)
-@{
- size_t len = strlen (s);
- wchar_t *result = malloc ((len + 1) * sizeof (wchar_t));
- wchar_t *wcp = result;
- wchar_t tmp[1];
- mbstate_t state;
- size_t nbytes;
-
- memset (&state, '\0', sizeof (state));
- while ((nbytes = mbrtowc (tmp, s, len, &state)) > 0)
- @{
- if (nbytes >= (size_t) -2)
- /* Invalid input string. */
- return NULL;
- *wcp++ = towupper (tmp[0]);
- len -= nbytes;
- s += nbytes;
- @}
- return result;
-@}
-@end smallexample
-
-The use of @code{mbrtowc} should be clear. A single wide character is
-stored in @code{@var{tmp}[0]}, and the number of consumed bytes is stored
-in the variable @var{nbytes}. If the conversion is successful, the
-uppercase variant of the wide character is stored in the @var{result}
-array and the pointer to the input string and the number of available
-bytes is adjusted.
-
-The only non-obvious thing about @code{mbrtowc} might be the way memory
-is allocated for the result. The above code uses the fact that there
-can never be more wide characters in the converted results than there are
-bytes in the multibyte input string. This method yields a pessimistic
-guess about the size of the result, and if many wide character strings
-have to be constructed this way or if the strings are long, the extra
-memory required to be allocated because the input string contains
-multibyte characters might be significant. The allocated memory block can
-be resized to the correct size before returning it, but a better solution
-might be to allocate just the right amount of space for the result right
-away. Unfortunately there is no function to compute the length of the wide
-character string directly from the multibyte string. There is, however, a
-function that does part of the work.
-
-@comment wchar.h
-@comment ISO
-@deftypefun size_t mbrlen (const char *restrict @var{s}, size_t @var{n}, mbstate_t *@var{ps})
-The @code{mbrlen} function (``multibyte restartable length'') computes
-the number of at most @var{n} bytes starting at @var{s}, which form the
-next valid and complete multibyte character.
-
-If the next multibyte character corresponds to the NUL wide character,
-the return value is @math{0}. If the next @var{n} bytes form a valid
-multibyte character, the number of bytes belonging to this multibyte
-character byte sequence is returned.
-
-If the first @var{n} bytes possibly form a valid multibyte
-character but the character is incomplete, the return value is
-@code{(size_t) -2}. Otherwise the multibyte character sequence is invalid
-and the return value is @code{(size_t) -1}.
-
-The multibyte sequence is interpreted in the state represented by the
-object pointed to by @var{ps}. If @var{ps} is a null pointer, a state
-object local to @code{mbrlen} is used.
-
-@pindex wchar.h
-@code{mbrlen} was introduced in @w{Amendment 1} to @w{ISO C90} and
-is declared in @file{wchar.h}.
-@end deftypefun
-
-The attentive reader now will note that @code{mbrlen} can be implemented
-as
-
-@smallexample
-mbrtowc (NULL, s, n, ps != NULL ? ps : &internal)
-@end smallexample
-
-This is true and in fact is mentioned in the official specification.
-How can this function be used to determine the length of the wide
-character string created from a multibyte character string? It is not
-directly usable, but we can define a function @code{mbslen} using it:
-
-@smallexample
-size_t
-mbslen (const char *s)
-@{
- mbstate_t state;
- size_t result = 0;
- size_t nbytes;
- memset (&state, '\0', sizeof (state));
- while ((nbytes = mbrlen (s, MB_LEN_MAX, &state)) > 0)
- @{
- if (nbytes >= (size_t) -2)
- /* @r{Something is wrong.} */
- return (size_t) -1;
- s += nbytes;
- ++result;
- @}
- return result;
-@}
-@end smallexample
-
-This function simply calls @code{mbrlen} for each multibyte character
-in the string and counts the number of function calls. Please note that
-we here use @code{MB_LEN_MAX} as the size argument in the @code{mbrlen}
-call. This is acceptable since a) this value is larger then the length of
-the longest multibyte character sequence and b) we know that the string
-@var{s} ends with a NUL byte, which cannot be part of any other multibyte
-character sequence but the one representing the NUL wide character.
-Therefore, the @code{mbrlen} function will never read invalid memory.
-
-Now that this function is available (just to make this clear, this
-function is @emph{not} part of the GNU C library) we can compute the
-number of wide character required to store the converted multibyte
-character string @var{s} using
-
-@smallexample
-wcs_bytes = (mbslen (s) + 1) * sizeof (wchar_t);
-@end smallexample
-
-Please note that the @code{mbslen} function is quite inefficient. The
-implementation of @code{mbstouwcs} with @code{mbslen} would have to
-perform the conversion of the multibyte character input string twice, and
-this conversion might be quite expensive. So it is necessary to think
-about the consequences of using the easier but imprecise method before
-doing the work twice.
-
-@comment wchar.h
-@comment ISO
-@deftypefun size_t wcrtomb (char *restrict @var{s}, wchar_t @var{wc}, mbstate_t *restrict @var{ps})
-The @code{wcrtomb} function (``wide character restartable to
-multibyte'') converts a single wide character into a multibyte string
-corresponding to that wide character.
-
-If @var{s} is a null pointer, the function resets the state stored in
-the objects pointed to by @var{ps} (or the internal @code{mbstate_t}
-object) to the initial state. This can also be achieved by a call like
-this:
-
-@smallexample
-wcrtombs (temp_buf, L'\0', ps)
-@end smallexample
-
-@noindent
-since, if @var{s} is a null pointer, @code{wcrtomb} performs as if it
-writes into an internal buffer, which is guaranteed to be large enough.
-
-If @var{wc} is the NUL wide character, @code{wcrtomb} emits, if
-necessary, a shift sequence to get the state @var{ps} into the initial
-state followed by a single NUL byte, which is stored in the string
-@var{s}.
-
-Otherwise a byte sequence (possibly including shift sequences) is written
-into the string @var{s}. This only happens if @var{wc} is a valid wide
-character (i.e., it has a multibyte representation in the character set
-selected by locale of the @code{LC_CTYPE} category). If @var{wc} is no
-valid wide character, nothing is stored in the strings @var{s},
-@code{errno} is set to @code{EILSEQ}, the conversion state in @var{ps}
-is undefined and the return value is @code{(size_t) -1}.
-
-If no error occurred the function returns the number of bytes stored in
-the string @var{s}. This includes all bytes representing shift
-sequences.
-
-One word about the interface of the function: there is no parameter
-specifying the length of the array @var{s}. Instead the function
-assumes that there are at least @code{MB_CUR_MAX} bytes available since
-this is the maximum length of any byte sequence representing a single
-character. So the caller has to make sure that there is enough space
-available, otherwise buffer overruns can occur.
-
-@pindex wchar.h
-@code{wcrtomb} was introduced in @w{Amendment 1} to @w{ISO C90} and is
-declared in @file{wchar.h}.
-@end deftypefun
-
-Using @code{wcrtomb} is as easy as using @code{mbrtowc}. The following
-example appends a wide character string to a multibyte character string.
-Again, the code is not really useful (or correct), it is simply here to
-demonstrate the use and some problems.
-
-@smallexample
-char *
-mbscatwcs (char *s, size_t len, const wchar_t *ws)
-@{
- mbstate_t state;
- /* @r{Find the end of the existing string.} */
- char *wp = strchr (s, '\0');
- len -= wp - s;
- memset (&state, '\0', sizeof (state));
- do
- @{
- size_t nbytes;
- if (len < MB_CUR_LEN)
- @{
- /* @r{We cannot guarantee that the next}
- @r{character fits into the buffer, so}
- @r{return an error.} */
- errno = E2BIG;
- return NULL;
- @}
- nbytes = wcrtomb (wp, *ws, &state);
- if (nbytes == (size_t) -1)
- /* @r{Error in the conversion.} */
- return NULL;
- len -= nbytes;
- wp += nbytes;
- @}
- while (*ws++ != L'\0');
- return s;
-@}
-@end smallexample
-
-First the function has to find the end of the string currently in the
-array @var{s}. The @code{strchr} call does this very efficiently since a
-requirement for multibyte character representations is that the NUL byte
-is never used except to represent itself (and in this context, the end
-of the string).
-
-After initializing the state object the loop is entered where the first
-task is to make sure there is enough room in the array @var{s}. We
-abort if there are not at least @code{MB_CUR_LEN} bytes available. This
-is not always optimal but we have no other choice. We might have less
-than @code{MB_CUR_LEN} bytes available but the next multibyte character
-might also be only one byte long. At the time the @code{wcrtomb} call
-returns it is too late to decide whether the buffer was large enough. If
-this solution is unsuitable, there is a very slow but more accurate
-solution.
-
-@smallexample
- @dots{}
- if (len < MB_CUR_LEN)
- @{
- mbstate_t temp_state;
- memcpy (&temp_state, &state, sizeof (state));
- if (wcrtomb (NULL, *ws, &temp_state) > len)
- @{
- /* @r{We cannot guarantee that the next}
- @r{character fits into the buffer, so}
- @r{return an error.} */
- errno = E2BIG;
- return NULL;
- @}
- @}
- @dots{}
-@end smallexample
-
-Here we perform the conversion that might overflow the buffer so that
-we are afterwards in the position to make an exact decision about the
-buffer size. Please note the @code{NULL} argument for the destination
-buffer in the new @code{wcrtomb} call; since we are not interested in the
-converted text at this point, this is a nice way to express this. The
-most unusual thing about this piece of code certainly is the duplication
-of the conversion state object, but if a change of the state is necessary
-to emit the next multibyte character, we want to have the same shift state
-change performed in the real conversion. Therefore, we have to preserve
-the initial shift state information.
-
-There are certainly many more and even better solutions to this problem.
-This example is only provided for educational purposes.
-
-@node Converting Strings
-@subsection Converting Multibyte and Wide Character Strings
-
-The functions described in the previous section only convert a single
-character at a time. Most operations to be performed in real-world
-programs include strings and therefore the @w{ISO C} standard also
-defines conversions on entire strings. However, the defined set of
-functions is quite limited; therefore, the GNU C library contains a few
-extensions that can help in some important situations.
-
-@comment wchar.h
-@comment ISO
-@deftypefun size_t mbsrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
-The @code{mbsrtowcs} function (``multibyte string restartable to wide
-character string'') converts an NUL-terminated multibyte character
-string at @code{*@var{src}} into an equivalent wide character string,
-including the NUL wide character at the end. The conversion is started
-using the state information from the object pointed to by @var{ps} or
-from an internal object of @code{mbsrtowcs} if @var{ps} is a null
-pointer. Before returning, the state object is updated to match the state
-after the last converted character. The state is the initial state if the
-terminating NUL byte is reached and converted.
-
-If @var{dst} is not a null pointer, the result is stored in the array
-pointed to by @var{dst}; otherwise, the conversion result is not
-available since it is stored in an internal buffer.
-
-If @var{len} wide characters are stored in the array @var{dst} before
-reaching the end of the input string, the conversion stops and @var{len}
-is returned. If @var{dst} is a null pointer, @var{len} is never checked.
-
-Another reason for a premature return from the function call is if the
-input string contains an invalid multibyte sequence. In this case the
-global variable @code{errno} is set to @code{EILSEQ} and the function
-returns @code{(size_t) -1}.
-
-@c XXX The ISO C9x draft seems to have a problem here. It says that PS
-@c is not updated if DST is NULL. This is not said straightforward and
-@c none of the other functions is described like this. It would make sense
-@c to define the function this way but I don't think it is meant like this.
-
-In all other cases the function returns the number of wide characters
-converted during this call. If @var{dst} is not null, @code{mbsrtowcs}
-stores in the pointer pointed to by @var{src} either a null pointer (if
-the NUL byte in the input string was reached) or the address of the byte
-following the last converted multibyte character.
-
-@pindex wchar.h
-@code{mbsrtowcs} was introduced in @w{Amendment 1} to @w{ISO C90} and is
-declared in @file{wchar.h}.
-@end deftypefun
-
-The definition of the @code{mbsrtowcs} function has one important
-limitation. The requirement that @var{dst} has to be a NUL-terminated
-string provides problems if one wants to convert buffers with text. A
-buffer is normally no collection of NUL-terminated strings but instead a
-continuous collection of lines, separated by newline characters. Now
-assume that a function to convert one line from a buffer is needed. Since
-the line is not NUL-terminated, the source pointer cannot directly point
-into the unmodified text buffer. This means, either one inserts the NUL
-byte at the appropriate place for the time of the @code{mbsrtowcs}
-function call (which is not doable for a read-only buffer or in a
-multi-threaded application) or one copies the line in an extra buffer
-where it can be terminated by a NUL byte. Note that it is not in general
-possible to limit the number of characters to convert by setting the
-parameter @var{len} to any specific value. Since it is not known how
-many bytes each multibyte character sequence is in length, one can only
-guess.
-
-@cindex stateful
-There is still a problem with the method of NUL-terminating a line right
-after the newline character, which could lead to very strange results.
-As said in the description of the @code{mbsrtowcs} function above the
-conversion state is guaranteed to be in the initial shift state after
-processing the NUL byte at the end of the input string. But this NUL
-byte is not really part of the text (i.e., the conversion state after
-the newline in the original text could be something different than the
-initial shift state and therefore the first character of the next line
-is encoded using this state). But the state in question is never
-accessible to the user since the conversion stops after the NUL byte
-(which resets the state). Most stateful character sets in use today
-require that the shift state after a newline be the initial state--but
-this is not a strict guarantee. Therefore, simply NUL-terminating a
-piece of a running text is not always an adequate solution and,
-therefore, should never be used in generally used code.
-
-The generic conversion interface (@pxref{Generic Charset Conversion})
-does not have this limitation (it simply works on buffers, not
-strings), and the GNU C library contains a set of functions that take
-additional parameters specifying the maximal number of bytes that are
-consumed from the input string. This way the problem of
-@code{mbsrtowcs}'s example above could be solved by determining the line
-length and passing this length to the function.
-
-@comment wchar.h
-@comment ISO
-@deftypefun size_t wcsrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
-The @code{wcsrtombs} function (``wide character string restartable to
-multibyte string'') converts the NUL-terminated wide character string at
-@code{*@var{src}} into an equivalent multibyte character string and
-stores the result in the array pointed to by @var{dst}. The NUL wide
-character is also converted. The conversion starts in the state
-described in the object pointed to by @var{ps} or by a state object
-locally to @code{wcsrtombs} in case @var{ps} is a null pointer. If
-@var{dst} is a null pointer, the conversion is performed as usual but the
-result is not available. If all characters of the input string were
-successfully converted and if @var{dst} is not a null pointer, the
-pointer pointed to by @var{src} gets assigned a null pointer.
-
-If one of the wide characters in the input string has no valid multibyte
-character equivalent, the conversion stops early, sets the global
-variable @code{errno} to @code{EILSEQ}, and returns @code{(size_t) -1}.
-
-Another reason for a premature stop is if @var{dst} is not a null
-pointer and the next converted character would require more than
-@var{len} bytes in total to the array @var{dst}. In this case (and if
-@var{dest} is not a null pointer) the pointer pointed to by @var{src} is
-assigned a value pointing to the wide character right after the last one
-successfully converted.
-
-Except in the case of an encoding error the return value of the
-@code{wcsrtombs} function is the number of bytes in all the multibyte
-character sequences stored in @var{dst}. Before returning the state in
-the object pointed to by @var{ps} (or the internal object in case
-@var{ps} is a null pointer) is updated to reflect the state after the
-last conversion. The state is the initial shift state in case the
-terminating NUL wide character was converted.
-
-@pindex wchar.h
-The @code{wcsrtombs} function was introduced in @w{Amendment 1} to
-@w{ISO C90} and is declared in @file{wchar.h}.
-@end deftypefun
-
-The restriction mentioned above for the @code{mbsrtowcs} function applies
-here also. There is no possibility of directly controlling the number of
-input characters. One has to place the NUL wide character at the correct
-place or control the consumed input indirectly via the available output
-array size (the @var{len} parameter).
-
-@comment wchar.h
-@comment GNU
-@deftypefun size_t mbsnrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{nmc}, size_t @var{len}, mbstate_t *restrict @var{ps})
-The @code{mbsnrtowcs} function is very similar to the @code{mbsrtowcs}
-function. All the parameters are the same except for @var{nmc}, which is
-new. The return value is the same as for @code{mbsrtowcs}.
-
-This new parameter specifies how many bytes at most can be used from the
-multibyte character string. In other words, the multibyte character
-string @code{*@var{src}} need not be NUL-terminated. But if a NUL byte
-is found within the @var{nmc} first bytes of the string, the conversion
-stops here.
-
-This function is a GNU extension. It is meant to work around the
-problems mentioned above. Now it is possible to convert a buffer with
-multibyte character text piece for piece without having to care about
-inserting NUL bytes and the effect of NUL bytes on the conversion state.
-@end deftypefun
-
-A function to convert a multibyte string into a wide character string
-and display it could be written like this (this is not a really useful
-example):
-
-@smallexample
-void
-showmbs (const char *src, FILE *fp)
-@{
- mbstate_t state;
- int cnt = 0;
- memset (&state, '\0', sizeof (state));
- while (1)
- @{
- wchar_t linebuf[100];
- const char *endp = strchr (src, '\n');
- size_t n;
-
- /* @r{Exit if there is no more line.} */
- if (endp == NULL)
- break;
-
- n = mbsnrtowcs (linebuf, &src, endp - src, 99, &state);
- linebuf[n] = L'\0';
- fprintf (fp, "line %d: \"%S\"\n", linebuf);
- @}
-@}
-@end smallexample
-
-There is no problem with the state after a call to @code{mbsnrtowcs}.
-Since we don't insert characters in the strings that were not in there
-right from the beginning and we use @var{state} only for the conversion
-of the given buffer, there is no problem with altering the state.
-
-@comment wchar.h
-@comment GNU
-@deftypefun size_t wcsnrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{nwc}, size_t @var{len}, mbstate_t *restrict @var{ps})
-The @code{wcsnrtombs} function implements the conversion from wide
-character strings to multibyte character strings. It is similar to
-@code{wcsrtombs} but, just like @code{mbsnrtowcs}, it takes an extra
-parameter, which specifies the length of the input string.
-
-No more than @var{nwc} wide characters from the input string
-@code{*@var{src}} are converted. If the input string contains a NUL
-wide character in the first @var{nwc} characters, the conversion stops at
-this place.
-
-The @code{wcsnrtombs} function is a GNU extension and just like
-@code{mbsnrtowcs} helps in situations where no NUL-terminated input
-strings are available.
-@end deftypefun
-
-
-@node Multibyte Conversion Example
-@subsection A Complete Multibyte Conversion Example
-
-The example programs given in the last sections are only brief and do
-not contain all the error checking, etc. Presented here is a complete
-and documented example. It features the @code{mbrtowc} function but it
-should be easy to derive versions using the other functions.
-
-@smallexample
-int
-file_mbsrtowcs (int input, int output)
-@{
- /* @r{Note the use of @code{MB_LEN_MAX}.}
- @r{@code{MB_CUR_MAX} cannot portably be used here.} */
- char buffer[BUFSIZ + MB_LEN_MAX];
- mbstate_t state;
- int filled = 0;
- int eof = 0;
-
- /* @r{Initialize the state.} */
- memset (&state, '\0', sizeof (state));
-
- while (!eof)
- @{
- ssize_t nread;
- ssize_t nwrite;
- char *inp = buffer;
- wchar_t outbuf[BUFSIZ];
- wchar_t *outp = outbuf;
-
- /* @r{Fill up the buffer from the input file.} */
- nread = read (input, buffer + filled, BUFSIZ);
- if (nread < 0)
- @{
- perror ("read");
- return 0;
- @}
- /* @r{If we reach end of file, make a note to read no more.} */
- if (nread == 0)
- eof = 1;
-
- /* @r{@code{filled} is now the number of bytes in @code{buffer}.} */
- filled += nread;
-
- /* @r{Convert those bytes to wide characters--as many as we can.} */
- while (1)
- @{
- size_t thislen = mbrtowc (outp, inp, filled, &state);
- /* @r{Stop converting at invalid character;}
- @r{this can mean we have read just the first part}
- @r{of a valid character.} */
- if (thislen == (size_t) -1)
- break;
- /* @r{We want to handle embedded NUL bytes}
- @r{but the return value is 0. Correct this.} */
- if (thislen == 0)
- thislen = 1;
- /* @r{Advance past this character.} */
- inp += thislen;
- filled -= thislen;
- ++outp;
- @}
-
- /* @r{Write the wide characters we just made.} */
- nwrite = write (output, outbuf,
- (outp - outbuf) * sizeof (wchar_t));
- if (nwrite < 0)
- @{
- perror ("write");
- return 0;
- @}
-
- /* @r{See if we have a @emph{real} invalid character.} */
- if ((eof && filled > 0) || filled >= MB_CUR_MAX)
- @{
- error (0, 0, "invalid multibyte character");
- return 0;
- @}
-
- /* @r{If any characters must be carried forward,}
- @r{put them at the beginning of @code{buffer}.} */
- if (filled > 0)
- memmove (inp, buffer, filled);
- @}
-
- return 1;
-@}
-@end smallexample
-
-
-@node Non-reentrant Conversion
-@section Non-reentrant Conversion Function
-
-The functions described in the previous chapter are defined in
-@w{Amendment 1} to @w{ISO C90}, but the original @w{ISO C90} standard
-also contained functions for character set conversion. The reason that
-these original functions are not described first is that they are almost
-entirely useless.
-
-The problem is that all the conversion functions described in the
-original @w{ISO C90} use a local state. Using a local state implies that
-multiple conversions at the same time (not only when using threads)
-cannot be done, and that you cannot first convert single characters and
-then strings since you cannot tell the conversion functions which state
-to use.
-
-These original functions are therefore usable only in a very limited set
-of situations. One must complete converting the entire string before
-starting a new one, and each string/text must be converted with the same
-function (there is no problem with the library itself; it is guaranteed
-that no library function changes the state of any of these functions).
-@strong{For the above reasons it is highly requested that the functions
-described in the previous section be used in place of non-reentrant
-conversion functions.}
-
-@menu
-* Non-reentrant Character Conversion:: Non-reentrant Conversion of Single
- Characters.
-* Non-reentrant String Conversion:: Non-reentrant Conversion of Strings.
-* Shift State:: States in Non-reentrant Functions.
-@end menu
-
-@node Non-reentrant Character Conversion
-@subsection Non-reentrant Conversion of Single Characters
-
-@comment stdlib.h
-@comment ISO
-@deftypefun int mbtowc (wchar_t *restrict @var{result}, const char *restrict @var{string}, size_t @var{size})
-The @code{mbtowc} (``multibyte to wide character'') function when called
-with non-null @var{string} converts the first multibyte character
-beginning at @var{string} to its corresponding wide character code. It
-stores the result in @code{*@var{result}}.
-
-@code{mbtowc} never examines more than @var{size} bytes. (The idea is
-to supply for @var{size} the number of bytes of data you have in hand.)
-
-@code{mbtowc} with non-null @var{string} distinguishes three
-possibilities: the first @var{size} bytes at @var{string} start with
-valid multibyte characters, they start with an invalid byte sequence or
-just part of a character, or @var{string} points to an empty string (a
-null character).
-
-For a valid multibyte character, @code{mbtowc} converts it to a wide
-character and stores that in @code{*@var{result}}, and returns the
-number of bytes in that character (always at least @math{1} and never
-more than @var{size}).
-
-For an invalid byte sequence, @code{mbtowc} returns @math{-1}. For an
-empty string, it returns @math{0}, also storing @code{'\0'} in
-@code{*@var{result}}.
-
-If the multibyte character code uses shift characters, then
-@code{mbtowc} maintains and updates a shift state as it scans. If you
-call @code{mbtowc} with a null pointer for @var{string}, that
-initializes the shift state to its standard initial value. It also
-returns nonzero if the multibyte character code in use actually has a
-shift state. @xref{Shift State}.
-@end deftypefun
-
-@comment stdlib.h
-@comment ISO
-@deftypefun int wctomb (char *@var{string}, wchar_t @var{wchar})
-The @code{wctomb} (``wide character to multibyte'') function converts
-the wide character code @var{wchar} to its corresponding multibyte
-character sequence, and stores the result in bytes starting at
-@var{string}. At most @code{MB_CUR_MAX} characters are stored.
-
-@code{wctomb} with non-null @var{string} distinguishes three
-possibilities for @var{wchar}: a valid wide character code (one that can
-be translated to a multibyte character), an invalid code, and
-@code{L'\0'}.
-
-Given a valid code, @code{wctomb} converts it to a multibyte character,
-storing the bytes starting at @var{string}. Then it returns the number
-of bytes in that character (always at least @math{1} and never more
-than @code{MB_CUR_MAX}).
-
-If @var{wchar} is an invalid wide character code, @code{wctomb} returns
-@math{-1}. If @var{wchar} is @code{L'\0'}, it returns @code{0}, also
-storing @code{'\0'} in @code{*@var{string}}.
-
-If the multibyte character code uses shift characters, then
-@code{wctomb} maintains and updates a shift state as it scans. If you
-call @code{wctomb} with a null pointer for @var{string}, that
-initializes the shift state to its standard initial value. It also
-returns nonzero if the multibyte character code in use actually has a
-shift state. @xref{Shift State}.
-
-Calling this function with a @var{wchar} argument of zero when
-@var{string} is not null has the side-effect of reinitializing the
-stored shift state @emph{as well as} storing the multibyte character
-@code{'\0'} and returning @math{0}.
-@end deftypefun
-
-Similar to @code{mbrlen} there is also a non-reentrant function that
-computes the length of a multibyte character. It can be defined in
-terms of @code{mbtowc}.
-
-@comment stdlib.h
-@comment ISO
-@deftypefun int mblen (const char *@var{string}, size_t @var{size})
-The @code{mblen} function with a non-null @var{string} argument returns
-the number of bytes that make up the multibyte character beginning at
-@var{string}, never examining more than @var{size} bytes. (The idea is
-to supply for @var{size} the number of bytes of data you have in hand.)
-
-The return value of @code{mblen} distinguishes three possibilities: the
-first @var{size} bytes at @var{string} start with valid multibyte
-characters, they start with an invalid byte sequence or just part of a
-character, or @var{string} points to an empty string (a null character).
-
-For a valid multibyte character, @code{mblen} returns the number of
-bytes in that character (always at least @code{1} and never more than
-@var{size}). For an invalid byte sequence, @code{mblen} returns
-@math{-1}. For an empty string, it returns @math{0}.
-
-If the multibyte character code uses shift characters, then @code{mblen}
-maintains and updates a shift state as it scans. If you call
-@code{mblen} with a null pointer for @var{string}, that initializes the
-shift state to its standard initial value. It also returns a nonzero
-value if the multibyte character code in use actually has a shift state.
-@xref{Shift State}.
-
-@pindex stdlib.h
-The function @code{mblen} is declared in @file{stdlib.h}.
-@end deftypefun
-
-
-@node Non-reentrant String Conversion
-@subsection Non-reentrant Conversion of Strings
-
-For convenience the @w{ISO C90} standard also defines functions to
-convert entire strings instead of single characters. These functions
-suffer from the same problems as their reentrant counterparts from
-@w{Amendment 1} to @w{ISO C90}; see @ref{Converting Strings}.
-
-@comment stdlib.h
-@comment ISO
-@deftypefun size_t mbstowcs (wchar_t *@var{wstring}, const char *@var{string}, size_t @var{size})
-The @code{mbstowcs} (``multibyte string to wide character string'')
-function converts the null-terminated string of multibyte characters
-@var{string} to an array of wide character codes, storing not more than
-@var{size} wide characters into the array beginning at @var{wstring}.
-The terminating null character counts towards the size, so if @var{size}
-is less than the actual number of wide characters resulting from
-@var{string}, no terminating null character is stored.
-
-The conversion of characters from @var{string} begins in the initial
-shift state.
-
-If an invalid multibyte character sequence is found, the @code{mbstowcs}
-function returns a value of @math{-1}. Otherwise, it returns the number
-of wide characters stored in the array @var{wstring}. This number does
-not include the terminating null character, which is present if the
-number is less than @var{size}.
-
-Here is an example showing how to convert a string of multibyte
-characters, allocating enough space for the result.
-
-@smallexample
-wchar_t *
-mbstowcs_alloc (const char *string)
-@{
- size_t size = strlen (string) + 1;
- wchar_t *buf = xmalloc (size * sizeof (wchar_t));
-
- size = mbstowcs (buf, string, size);
- if (size == (size_t) -1)
- return NULL;
- buf = xrealloc (buf, (size + 1) * sizeof (wchar_t));
- return buf;
-@}
-@end smallexample
-
-@end deftypefun
-
-@comment stdlib.h
-@comment ISO
-@deftypefun size_t wcstombs (char *@var{string}, const wchar_t *@var{wstring}, size_t @var{size})
-The @code{wcstombs} (``wide character string to multibyte string'')
-function converts the null-terminated wide character array @var{wstring}
-into a string containing multibyte characters, storing not more than
-@var{size} bytes starting at @var{string}, followed by a terminating
-null character if there is room. The conversion of characters begins in
-the initial shift state.
-
-The terminating null character counts towards the size, so if @var{size}
-is less than or equal to the number of bytes needed in @var{wstring}, no
-terminating null character is stored.
-
-If a code that does not correspond to a valid multibyte character is
-found, the @code{wcstombs} function returns a value of @math{-1}.
-Otherwise, the return value is the number of bytes stored in the array
-@var{string}. This number does not include the terminating null character,
-which is present if the number is less than @var{size}.
-@end deftypefun
-
-@node Shift State
-@subsection States in Non-reentrant Functions
-
-In some multibyte character codes, the @emph{meaning} of any particular
-byte sequence is not fixed; it depends on what other sequences have come
-earlier in the same string. Typically there are just a few sequences that
-can change the meaning of other sequences; these few are called
-@dfn{shift sequences} and we say that they set the @dfn{shift state} for
-other sequences that follow.
-
-To illustrate shift state and shift sequences, suppose we decide that
-the sequence @code{0200} (just one byte) enters Japanese mode, in which
-pairs of bytes in the range from @code{0240} to @code{0377} are single
-characters, while @code{0201} enters Latin-1 mode, in which single bytes
-in the range from @code{0240} to @code{0377} are characters, and
-interpreted according to the ISO Latin-1 character set. This is a
-multibyte code that has two alternative shift states (``Japanese mode''
-and ``Latin-1 mode''), and two shift sequences that specify particular
-shift states.
-
-When the multibyte character code in use has shift states, then
-@code{mblen}, @code{mbtowc}, and @code{wctomb} must maintain and update
-the current shift state as they scan the string. To make this work
-properly, you must follow these rules:
-
-@itemize @bullet
-@item
-Before starting to scan a string, call the function with a null pointer
-for the multibyte character address---for example, @code{mblen (NULL,
-0)}. This initializes the shift state to its standard initial value.
-
-@item
-Scan the string one character at a time, in order. Do not ``back up''
-and rescan characters already scanned, and do not intersperse the
-processing of different strings.
-@end itemize
-
-Here is an example of using @code{mblen} following these rules:
-
-@smallexample
-void
-scan_string (char *s)
-@{
- int length = strlen (s);
-
- /* @r{Initialize shift state.} */
- mblen (NULL, 0);
-
- while (1)
- @{
- int thischar = mblen (s, length);
- /* @r{Deal with end of string and invalid characters.} */
- if (thischar == 0)
- break;
- if (thischar == -1)
- @{
- error ("invalid multibyte character");
- break;
- @}
- /* @r{Advance past this character.} */
- s += thischar;
- length -= thischar;
- @}
-@}
-@end smallexample
-
-The functions @code{mblen}, @code{mbtowc} and @code{wctomb} are not
-reentrant when using a multibyte code that uses a shift state. However,
-no other library functions call these functions, so you don't have to
-worry that the shift state will be changed mysteriously.
-
-
-@node Generic Charset Conversion
-@section Generic Charset Conversion
-
-The conversion functions mentioned so far in this chapter all had in
-common that they operate on character sets that are not directly
-specified by the functions. The multibyte encoding used is specified by
-the currently selected locale for the @code{LC_CTYPE} category. The
-wide character set is fixed by the implementation (in the case of GNU C
-library it is always UCS-4 encoded @w{ISO 10646}.
-
-This has of course several problems when it comes to general character
-conversion:
-
-@itemize @bullet
-@item
-For every conversion where neither the source nor the destination
-character set is the character set of the locale for the @code{LC_CTYPE}
-category, one has to change the @code{LC_CTYPE} locale using
-@code{setlocale}.
-
-Changing the @code{LC_TYPE} locale introduces major problems for the rest
-of the programs since several more functions (e.g., the character
-classification functions, @pxref{Classification of Characters}) use the
-@code{LC_CTYPE} category.
-
-@item
-Parallel conversions to and from different character sets are not
-possible since the @code{LC_CTYPE} selection is global and shared by all
-threads.
-
-@item
-If neither the source nor the destination character set is the character
-set used for @code{wchar_t} representation, there is at least a two-step
-process necessary to convert a text using the functions above. One would
-have to select the source character set as the multibyte encoding,
-convert the text into a @code{wchar_t} text, select the destination
-character set as the multibyte encoding, and convert the wide character
-text to the multibyte (@math{=} destination) character set.
-
-Even if this is possible (which is not guaranteed) it is a very tiring
-work. Plus it suffers from the other two raised points even more due to
-the steady changing of the locale.
-@end itemize
-
-The XPG2 standard defines a completely new set of functions, which has
-none of these limitations. They are not at all coupled to the selected
-locales, and they have no constraints on the character sets selected for
-source and destination. Only the set of available conversions limits
-them. The standard does not specify that any conversion at all must be
-available. Such availability is a measure of the quality of the
-implementation.
-
-In the following text first the interface to @code{iconv} and then the
-conversion function, will be described. Comparisons with other
-implementations will show what obstacles stand in the way of portable
-applications. Finally, the implementation is described in so far as might
-interest the advanced user who wants to extend conversion capabilities.
-
-@menu
-* Generic Conversion Interface:: Generic Character Set Conversion Interface.
-* iconv Examples:: A complete @code{iconv} example.
-* Other iconv Implementations:: Some Details about other @code{iconv}
- Implementations.
-* glibc iconv Implementation:: The @code{iconv} Implementation in the GNU C
- library.
-@end menu
-
-@node Generic Conversion Interface
-@subsection Generic Character Set Conversion Interface
-
-This set of functions follows the traditional cycle of using a resource:
-open--use--close. The interface consists of three functions, each of
-which implements one step.
-
-Before the interfaces are described it is necessary to introduce a
-data type. Just like other open--use--close interfaces the functions
-introduced here work using handles and the @file{iconv.h} header
-defines a special type for the handles used.
-
-@comment iconv.h
-@comment XPG2
-@deftp {Data Type} iconv_t
-This data type is an abstract type defined in @file{iconv.h}. The user
-must not assume anything about the definition of this type; it must be
-completely opaque.
-
-Objects of this type can get assigned handles for the conversions using
-the @code{iconv} functions. The objects themselves need not be freed, but
-the conversions for which the handles stand for have to.
-@end deftp
-
-@noindent
-The first step is the function to create a handle.
-
-@comment iconv.h
-@comment XPG2
-@deftypefun iconv_t iconv_open (const char *@var{tocode}, const char *@var{fromcode})
-The @code{iconv_open} function has to be used before starting a
-conversion. The two parameters this function takes determine the
-source and destination character set for the conversion, and if the
-implementation has the possibility to perform such a conversion, the
-function returns a handle.
-
-If the wanted conversion is not available, the @code{iconv_open} function
-returns @code{(iconv_t) -1}. In this case the global variable
-@code{errno} can have the following values:
-
-@table @code
-@item EMFILE
-The process already has @code{OPEN_MAX} file descriptors open.
-@item ENFILE
-The system limit of open file is reached.
-@item ENOMEM
-Not enough memory to carry out the operation.
-@item EINVAL
-The conversion from @var{fromcode} to @var{tocode} is not supported.
-@end table
-
-It is not possible to use the same descriptor in different threads to
-perform independent conversions. The data structures associated
-with the descriptor include information about the conversion state.
-This must not be messed up by using it in different conversions.
-
-An @code{iconv} descriptor is like a file descriptor as for every use a
-new descriptor must be created. The descriptor does not stand for all
-of the conversions from @var{fromset} to @var{toset}.
-
-The GNU C library implementation of @code{iconv_open} has one
-significant extension to other implementations. To ease the extension
-of the set of available conversions, the implementation allows storing
-the necessary files with data and code in an arbitrary number of
-directories. How this extension must be written will be explained below
-(@pxref{glibc iconv Implementation}). Here it is only important to say
-that all directories mentioned in the @code{GCONV_PATH} environment
-variable are considered only if they contain a file @file{gconv-modules}.
-These directories need not necessarily be created by the system
-administrator. In fact, this extension is introduced to help users
-writing and using their own, new conversions. Of course, this does not
-work for security reasons in SUID binaries; in this case only the system
-directory is considered and this normally is
-@file{@var{prefix}/lib/gconv}. The @code{GCONV_PATH} environment
-variable is examined exactly once at the first call of the
-@code{iconv_open} function. Later modifications of the variable have no
-effect.
-
-@pindex iconv.h
-The @code{iconv_open} function was introduced early in the X/Open
-Portability Guide, @w{version 2}. It is supported by all commercial
-Unices as it is required for the Unix branding. However, the quality and
-completeness of the implementation varies widely. The @code{iconv_open}
-function is declared in @file{iconv.h}.
-@end deftypefun
-
-The @code{iconv} implementation can associate large data structure with
-the handle returned by @code{iconv_open}. Therefore, it is crucial to
-free all the resources once all conversions are carried out and the
-conversion is not needed anymore.
-
-@comment iconv.h
-@comment XPG2
-@deftypefun int iconv_close (iconv_t @var{cd})
-The @code{iconv_close} function frees all resources associated with the
-handle @var{cd}, which must have been returned by a successful call to
-the @code{iconv_open} function.
-
-If the function call was successful the return value is @math{0}.
-Otherwise it is @math{-1} and @code{errno} is set appropriately.
-Defined error are:
-
-@table @code
-@item EBADF
-The conversion descriptor is invalid.
-@end table
-
-@pindex iconv.h
-The @code{iconv_close} function was introduced together with the rest
-of the @code{iconv} functions in XPG2 and is declared in @file{iconv.h}.
-@end deftypefun
-
-The standard defines only one actual conversion function. This has,
-therefore, the most general interface: it allows conversion from one
-buffer to another. Conversion from a file to a buffer, vice versa, or
-even file to file can be implemented on top of it.
-
-@comment iconv.h
-@comment XPG2
-@deftypefun size_t iconv (iconv_t @var{cd}, char **@var{inbuf}, size_t *@var{inbytesleft}, char **@var{outbuf}, size_t *@var{outbytesleft})
-@cindex stateful
-The @code{iconv} function converts the text in the input buffer
-according to the rules associated with the descriptor @var{cd} and
-stores the result in the output buffer. It is possible to call the
-function for the same text several times in a row since for stateful
-character sets the necessary state information is kept in the data
-structures associated with the descriptor.
-
-The input buffer is specified by @code{*@var{inbuf}} and it contains
-@code{*@var{inbytesleft}} bytes. The extra indirection is necessary for
-communicating the used input back to the caller (see below). It is
-important to note that the buffer pointer is of type @code{char} and the
-length is measured in bytes even if the input text is encoded in wide
-characters.
-
-The output buffer is specified in a similar way. @code{*@var{outbuf}}
-points to the beginning of the buffer with at least
-@code{*@var{outbytesleft}} bytes room for the result. The buffer
-pointer again is of type @code{char} and the length is measured in
-bytes. If @var{outbuf} or @code{*@var{outbuf}} is a null pointer, the
-conversion is performed but no output is available.
-
-If @var{inbuf} is a null pointer, the @code{iconv} function performs the
-necessary action to put the state of the conversion into the initial
-state. This is obviously a no-op for non-stateful encodings, but if the
-encoding has a state, such a function call might put some byte sequences
-in the output buffer, which perform the necessary state changes. The
-next call with @var{inbuf} not being a null pointer then simply goes on
-from the initial state. It is important that the programmer never makes
-any assumption as to whether the conversion has to deal with states.
-Even if the input and output character sets are not stateful, the
-implementation might still have to keep states. This is due to the
-implementation chosen for the GNU C library as it is described below.
-Therefore an @code{iconv} call to reset the state should always be
-performed if some protocol requires this for the output text.
-
-The conversion stops for one of three reasons. The first is that all
-characters from the input buffer are converted. This actually can mean
-two things: either all bytes from the input buffer are consumed or
-there are some bytes at the end of the buffer that possibly can form a
-complete character but the input is incomplete. The second reason for a
-stop is that the output buffer is full. And the third reason is that
-the input contains invalid characters.
-
-In all of these cases the buffer pointers after the last successful
-conversion, for input and output buffer, are stored in @var{inbuf} and
-@var{outbuf}, and the available room in each buffer is stored in
-@var{inbytesleft} and @var{outbytesleft}.
-
-Since the character sets selected in the @code{iconv_open} call can be
-almost arbitrary, there can be situations where the input buffer contains
-valid characters, which have no identical representation in the output
-character set. The behavior in this situation is undefined. The
-@emph{current} behavior of the GNU C library in this situation is to
-return with an error immediately. This certainly is not the most
-desirable solution; therefore, future versions will provide better ones,
-but they are not yet finished.
-
-If all input from the input buffer is successfully converted and stored
-in the output buffer, the function returns the number of non-reversible
-conversions performed. In all other cases the return value is
-@code{(size_t) -1} and @code{errno} is set appropriately. In such cases
-the value pointed to by @var{inbytesleft} is nonzero.
-
-@table @code
-@item EILSEQ
-The conversion stopped because of an invalid byte sequence in the input.
-After the call, @code{*@var{inbuf}} points at the first byte of the
-invalid byte sequence.
-
-@item E2BIG
-The conversion stopped because it ran out of space in the output buffer.
-
-@item EINVAL
-The conversion stopped because of an incomplete byte sequence at the end
-of the input buffer.
-
-@item EBADF
-The @var{cd} argument is invalid.
-@end table
-
-@pindex iconv.h
-The @code{iconv} function was introduced in the XPG2 standard and is
-declared in the @file{iconv.h} header.
-@end deftypefun
-
-The definition of the @code{iconv} function is quite good overall. It
-provides quite flexible functionality. The only problems lie in the
-boundary cases, which are incomplete byte sequences at the end of the
-input buffer and invalid input. A third problem, which is not really
-a design problem, is the way conversions are selected. The standard
-does not say anything about the legitimate names, a minimal set of
-available conversions. We will see how this negatively impacts other
-implementations, as demonstrated below.
-
-@node iconv Examples
-@subsection A complete @code{iconv} example
-
-The example below features a solution for a common problem. Given that
-one knows the internal encoding used by the system for @code{wchar_t}
-strings, one often is in the position to read text from a file and store
-it in wide character buffers. One can do this using @code{mbsrtowcs},
-but then we run into the problems discussed above.
-
-@smallexample
-int
-file2wcs (int fd, const char *charset, wchar_t *outbuf, size_t avail)
-@{
- char inbuf[BUFSIZ];
- size_t insize = 0;
- char *wrptr = (char *) outbuf;
- int result = 0;
- iconv_t cd;
-
- cd = iconv_open ("WCHAR_T", charset);
- if (cd == (iconv_t) -1)
- @{
- /* @r{Something went wrong.} */
- if (errno == EINVAL)
- error (0, 0, "conversion from '%s' to wchar_t not available",
- charset);
- else
- perror ("iconv_open");
-
- /* @r{Terminate the output string.} */
- *outbuf = L'\0';
-
- return -1;
- @}
-
- while (avail > 0)
- @{
- size_t nread;
- size_t nconv;
- char *inptr = inbuf;
-
- /* @r{Read more input.} */
- nread = read (fd, inbuf + insize, sizeof (inbuf) - insize);
- if (nread == 0)
- @{
- /* @r{When we come here the file is completely read.}
- @r{This still could mean there are some unused}
- @r{characters in the @code{inbuf}. Put them back.} */
- if (lseek (fd, -insize, SEEK_CUR) == -1)
- result = -1;
-
- /* @r{Now write out the byte sequence to get into the}
- @r{initial state if this is necessary.} */
- iconv (cd, NULL, NULL, &wrptr, &avail);
-
- break;
- @}
- insize += nread;
-
- /* @r{Do the conversion.} */
- nconv = iconv (cd, &inptr, &insize, &wrptr, &avail);
- if (nconv == (size_t) -1)
- @{
- /* @r{Not everything went right. It might only be}
- @r{an unfinished byte sequence at the end of the}
- @r{buffer. Or it is a real problem.} */
- if (errno == EINVAL)
- /* @r{This is harmless. Simply move the unused}
- @r{bytes to the beginning of the buffer so that}
- @r{they can be used in the next round.} */
- memmove (inbuf, inptr, insize);
- else
- @{
- /* @r{It is a real problem. Maybe we ran out of}
- @r{space in the output buffer or we have invalid}
- @r{input. In any case back the file pointer to}
- @r{the position of the last processed byte.} */
- lseek (fd, -insize, SEEK_CUR);
- result = -1;
- break;
- @}
- @}
- @}
-
- /* @r{Terminate the output string.} */
- if (avail >= sizeof (wchar_t))
- *((wchar_t *) wrptr) = L'\0';
-
- if (iconv_close (cd) != 0)
- perror ("iconv_close");
-
- return (wchar_t *) wrptr - outbuf;
-@}
-@end smallexample
-
-@cindex stateful
-This example shows the most important aspects of using the @code{iconv}
-functions. It shows how successive calls to @code{iconv} can be used to
-convert large amounts of text. The user does not have to care about
-stateful encodings as the functions take care of everything.
-
-An interesting point is the case where @code{iconv} returns an error and
-@code{errno} is set to @code{EINVAL}. This is not really an error in the
-transformation. It can happen whenever the input character set contains
-byte sequences of more than one byte for some character and texts are not
-processed in one piece. In this case there is a chance that a multibyte
-sequence is cut. The caller can then simply read the remainder of the
-takes and feed the offending bytes together with new character from the
-input to @code{iconv} and continue the work. The internal state kept in
-the descriptor is @emph{not} unspecified after such an event as is the
-case with the conversion functions from the @w{ISO C} standard.
-
-The example also shows the problem of using wide character strings with
-@code{iconv}. As explained in the description of the @code{iconv}
-function above, the function always takes a pointer to a @code{char}
-array and the available space is measured in bytes. In the example, the
-output buffer is a wide character buffer; therefore, we use a local
-variable @var{wrptr} of type @code{char *}, which is used in the
-@code{iconv} calls.
-
-This looks rather innocent but can lead to problems on platforms that
-have tight restriction on alignment. Therefore the caller of @code{iconv}
-has to make sure that the pointers passed are suitable for access of
-characters from the appropriate character set. Since, in the
-above case, the input parameter to the function is a @code{wchar_t}
-pointer, this is the case (unless the user violates alignment when
-computing the parameter). But in other situations, especially when
-writing generic functions where one does not know what type of character
-set one uses and, therefore, treats text as a sequence of bytes, it might
-become tricky.
-
-@node Other iconv Implementations
-@subsection Some Details about other @code{iconv} Implementations
-
-This is not really the place to discuss the @code{iconv} implementation
-of other systems but it is necessary to know a bit about them to write
-portable programs. The above mentioned problems with the specification
-of the @code{iconv} functions can lead to portability issues.
-
-The first thing to notice is that, due to the large number of character
-sets in use, it is certainly not practical to encode the conversions
-directly in the C library. Therefore, the conversion information must
-come from files outside the C library. This is usually done in one or
-both of the following ways:
-
-@itemize @bullet
-@item
-The C library contains a set of generic conversion functions that can
-read the needed conversion tables and other information from data files.
-These files get loaded when necessary.
-
-This solution is problematic as it requires a great deal of effort to
-apply to all character sets (potentially an infinite set). The
-differences in the structure of the different character sets is so large
-that many different variants of the table-processing functions must be
-developed. In addition, the generic nature of these functions make them
-slower than specifically implemented functions.
-
-@item
-The C library only contains a framework that can dynamically load
-object files and execute the conversion functions contained therein.
-
-This solution provides much more flexibility. The C library itself
-contains only very little code and therefore reduces the general memory
-footprint. Also, with a documented interface between the C library and
-the loadable modules it is possible for third parties to extend the set
-of available conversion modules. A drawback of this solution is that
-dynamic loading must be available.
-@end itemize
-
-Some implementations in commercial Unices implement a mixture of these
-possibilities; the majority implement only the second solution. Using
-loadable modules moves the code out of the library itself and keeps
-the door open for extensions and improvements, but this design is also
-limiting on some platforms since not many platforms support dynamic
-loading in statically linked programs. On platforms without this
-capability it is therefore not possible to use this interface in
-statically linked programs. The GNU C library has, on ELF platforms, no
-problems with dynamic loading in these situations; therefore, this
-point is moot. The danger is that one gets acquainted with this
-situation and forgets about the restrictions on other systems.
-
-A second thing to know about other @code{iconv} implementations is that
-the number of available conversions is often very limited. Some
-implementations provide, in the standard release (not special
-international or developer releases), at most 100 to 200 conversion
-possibilities. This does not mean 200 different character sets are
-supported; for example, conversions from one character set to a set of 10
-others might count as 10 conversions. Together with the other direction
-this makes 20 conversion possibilities used up by one character set. One
-can imagine the thin coverage these platform provide. Some Unix vendors
-even provide only a handful of conversions, which renders them useless for
-almost all uses.
-
-This directly leads to a third and probably the most problematic point.
-The way the @code{iconv} conversion functions are implemented on all
-known Unix systems and the availability of the conversion functions from
-character set @math{@cal{A}} to @math{@cal{B}} and the conversion from
-@math{@cal{B}} to @math{@cal{C}} does @emph{not} imply that the
-conversion from @math{@cal{A}} to @math{@cal{C}} is available.
-
-This might not seem unreasonable and problematic at first, but it is a
-quite big problem as one will notice shortly after hitting it. To show
-the problem we assume to write a program that has to convert from
-@math{@cal{A}} to @math{@cal{C}}. A call like
-
-@smallexample
-cd = iconv_open ("@math{@cal{C}}", "@math{@cal{A}}");
-@end smallexample
-
-@noindent
-fails according to the assumption above. But what does the program
-do now? The conversion is necessary; therefore, simply giving up is not
-an option.
-
-This is a nuisance. The @code{iconv} function should take care of this.
-But how should the program proceed from here on? If it tries to convert
-to character set @math{@cal{B}}, first the two @code{iconv_open}
-calls
-
-@smallexample
-cd1 = iconv_open ("@math{@cal{B}}", "@math{@cal{A}}");
-@end smallexample
-
-@noindent
-and
-
-@smallexample
-cd2 = iconv_open ("@math{@cal{C}}", "@math{@cal{B}}");
-@end smallexample
-
-@noindent
-will succeed, but how to find @math{@cal{B}}?
-
-Unfortunately, the answer is: there is no general solution. On some
-systems guessing might help. On those systems most character sets can
-convert to and from UTF-8 encoded @w{ISO 10646} or Unicode text. Beside
-this only some very system-specific methods can help. Since the
-conversion functions come from loadable modules and these modules must
-be stored somewhere in the filesystem, one @emph{could} try to find them
-and determine from the available file which conversions are available
-and whether there is an indirect route from @math{@cal{A}} to
-@math{@cal{C}}.
-
-This example shows one of the design errors of @code{iconv} mentioned
-above. It should at least be possible to determine the list of available
-conversion programmatically so that if @code{iconv_open} says there is no
-such conversion, one could make sure this also is true for indirect
-routes.
-
-@node glibc iconv Implementation
-@subsection The @code{iconv} Implementation in the GNU C library
-
-After reading about the problems of @code{iconv} implementations in the
-last section it is certainly good to note that the implementation in
-the GNU C library has none of the problems mentioned above. What
-follows is a step-by-step analysis of the points raised above. The
-evaluation is based on the current state of the development (as of
-January 1999). The development of the @code{iconv} functions is not
-complete, but basic functionality has solidified.
-
-The GNU C library's @code{iconv} implementation uses shared loadable
-modules to implement the conversions. A very small number of
-conversions are built into the library itself but these are only rather
-trivial conversions.
-
-All the benefits of loadable modules are available in the GNU C library
-implementation. This is especially appealing since the interface is
-well documented (see below), and it, therefore, is easy to write new
-conversion modules. The drawback of using loadable objects is not a
-problem in the GNU C library, at least on ELF systems. Since the
-library is able to load shared objects even in statically linked
-binaries, static linking need not be forbidden in case one wants to use
-@code{iconv}.
-
-The second mentioned problem is the number of supported conversions.
-Currently, the GNU C library supports more than 150 character sets. The
-way the implementation is designed the number of supported conversions
-is greater than 22350 (@math{150} times @math{149}). If any conversion
-from or to a character set is missing, it can be added easily.
-
-Particularly impressive as it may be, this high number is due to the
-fact that the GNU C library implementation of @code{iconv} does not have
-the third problem mentioned above (i.e., whenever there is a conversion
-from a character set @math{@cal{A}} to @math{@cal{B}} and from
-@math{@cal{B}} to @math{@cal{C}} it is always possible to convert from
-@math{@cal{A}} to @math{@cal{C}} directly). If the @code{iconv_open}
-returns an error and sets @code{errno} to @code{EINVAL}, there is no
-known way, directly or indirectly, to perform the wanted conversion.
-
-@cindex triangulation
-Triangulation is achieved by providing for each character set a
-conversion from and to UCS-4 encoded @w{ISO 10646}. Using @w{ISO 10646}
-as an intermediate representation it is possible to @dfn{triangulate}
-(i.e., convert with an intermediate representation).
-
-There is no inherent requirement to provide a conversion to @w{ISO
-10646} for a new character set, and it is also possible to provide other
-conversions where neither source nor destination character set is @w{ISO
-10646}. The existing set of conversions is simply meant to cover all
-conversions that might be of interest.
-
-@cindex ISO-2022-JP
-@cindex EUC-JP
-All currently available conversions use the triangulation method above,
-making conversion run unnecessarily slow. If, for example, somebody
-often needs the conversion from ISO-2022-JP to EUC-JP, a quicker solution
-would involve direct conversion between the two character sets, skipping
-the input to @w{ISO 10646} first. The two character sets of interest
-are much more similar to each other than to @w{ISO 10646}.
-
-In such a situation one easily can write a new conversion and provide it
-as a better alternative. The GNU C library @code{iconv} implementation
-would automatically use the module implementing the conversion if it is
-specified to be more efficient.
-
-@subsubsection Format of @file{gconv-modules} files
-
-All information about the available conversions comes from a file named
-@file{gconv-modules}, which can be found in any of the directories along
-the @code{GCONV_PATH}. The @file{gconv-modules} files are line-oriented
-text files, where each of the lines has one of the following formats:
-
-@itemize @bullet
-@item
-If the first non-whitespace character is a @kbd{#} the line contains only
-comments and is ignored.
-
-@item
-Lines starting with @code{alias} define an alias name for a character
-set. Two more words are expected on the line. The first word
-defines the alias name, and the second defines the original name of the
-character set. The effect is that it is possible to use the alias name
-in the @var{fromset} or @var{toset} parameters of @code{iconv_open} and
-achieve the same result as when using the real character set name.
-
-This is quite important as a character set has often many different
-names. There is normally an official name but this need not correspond to
-the most popular name. Beside this many character sets have special
-names that are somehow constructed. For example, all character sets
-specified by the ISO have an alias of the form @code{ISO-IR-@var{nnn}}
-where @var{nnn} is the registration number. This allows programs that
-know about the registration number to construct character set names and
-use them in @code{iconv_open} calls. More on the available names and
-aliases follows below.
-
-@item
-Lines starting with @code{module} introduce an available conversion
-module. These lines must contain three or four more words.
-
-The first word specifies the source character set, the second word the
-destination character set of conversion implemented in this module, and
-the third word is the name of the loadable module. The filename is
-constructed by appending the usual shared object suffix (normally
-@file{.so}) and this file is then supposed to be found in the same
-directory the @file{gconv-modules} file is in. The last word on the line,
-which is optional, is a numeric value representing the cost of the
-conversion. If this word is missing, a cost of @math{1} is assumed. The
-numeric value itself does not matter that much; what counts are the
-relative values of the sums of costs for all possible conversion paths.
-Below is a more precise description of the use of the cost value.
-@end itemize
-
-Returning to the example above where one has written a module to directly
-convert from ISO-2022-JP to EUC-JP and back. All that has to be done is
-to put the new module, let its name be ISO2022JP-EUCJP.so, in a directory
-and add a file @file{gconv-modules} with the following content in the
-same directory:
-
-@smallexample
-module ISO-2022-JP// EUC-JP// ISO2022JP-EUCJP 1
-module EUC-JP// ISO-2022-JP// ISO2022JP-EUCJP 1
-@end smallexample
-
-To see why this is sufficient, it is necessary to understand how the
-conversion used by @code{iconv} (and described in the descriptor) is
-selected. The approach to this problem is quite simple.
-
-At the first call of the @code{iconv_open} function the program reads
-all available @file{gconv-modules} files and builds up two tables: one
-containing all the known aliases and another that contains the
-information about the conversions and which shared object implements
-them.
-
-@subsubsection Finding the conversion path in @code{iconv}
-
-The set of available conversions form a directed graph with weighted
-edges. The weights on the edges are the costs specified in the
-@file{gconv-modules} files. The @code{iconv_open} function uses an
-algorithm suitable for search for the best path in such a graph and so
-constructs a list of conversions that must be performed in succession
-to get the transformation from the source to the destination character
-set.
-
-Explaining why the above @file{gconv-modules} files allows the
-@code{iconv} implementation to resolve the specific ISO-2022-JP to
-EUC-JP conversion module instead of the conversion coming with the
-library itself is straightforward. Since the latter conversion takes two
-steps (from ISO-2022-JP to @w{ISO 10646} and then from @w{ISO 10646} to
-EUC-JP), the cost is @math{1+1 = 2}. The above @file{gconv-modules}
-file, however, specifies that the new conversion modules can perform this
-conversion with only the cost of @math{1}.
-
-A mysterious item about the @file{gconv-modules} file above (and also
-the file coming with the GNU C library) are the names of the character
-sets specified in the @code{module} lines. Why do almost all the names
-end in @code{//}? And this is not all: the names can actually be
-regular expressions. At this point in time this mystery should not be
-revealed, unless you have the relevant spell-casting materials: ashes
-from an original @w{DOS 6.2} boot disk burnt in effigy, a crucifix
-blessed by St.@: Emacs, assorted herbal roots from Central America, sand
-from Cebu, etc. Sorry! @strong{The part of the implementation where
-this is used is not yet finished. For now please simply follow the
-existing examples. It'll become clearer once it is. --drepper}
-
-A last remark about the @file{gconv-modules} is about the names not
-ending with @code{//}. A character set named @code{INTERNAL} is often
-mentioned. From the discussion above and the chosen name it should have
-become clear that this is the name for the representation used in the
-intermediate step of the triangulation. We have said that this is UCS-4
-but actually that is not quite right. The UCS-4 specification also
-includes the specification of the byte ordering used. Since a UCS-4 value
-consists of four bytes, a stored value is effected by byte ordering. The
-internal representation is @emph{not} the same as UCS-4 in case the byte
-ordering of the processor (or at least the running process) is not the
-same as the one required for UCS-4. This is done for performance reasons
-as one does not want to perform unnecessary byte-swapping operations if
-one is not interested in actually seeing the result in UCS-4. To avoid
-trouble with endianness, the internal representation consistently is named
-@code{INTERNAL} even on big-endian systems where the representations are
-identical.
-
-@subsubsection @code{iconv} module data structures
-
-So far this section has described how modules are located and considered
-to be used. What remains to be described is the interface of the modules
-so that one can write new ones. This section describes the interface as
-it is in use in January 1999. The interface will change a bit in the
-future but, with luck, only in an upwardly compatible way.
-
-The definitions necessary to write new modules are publicly available
-in the non-standard header @file{gconv.h}. The following text,
-therefore, describes the definitions from this header file. First,
-however, it is necessary to get an overview.
-
-From the perspective of the user of @code{iconv} the interface is quite
-simple: the @code{iconv_open} function returns a handle that can be used
-in calls to @code{iconv}, and finally the handle is freed with a call to
-@code{iconv_close}. The problem is that the handle has to be able to
-represent the possibly long sequences of conversion steps and also the
-state of each conversion since the handle is all that is passed to the
-@code{iconv} function. Therefore, the data structures are really the
-elements necessary to understanding the implementation.
-
-We need two different kinds of data structures. The first describes the
-conversion and the second describes the state etc. There are really two
-type definitions like this in @file{gconv.h}.
-@pindex gconv.h
-
-@comment gconv.h
-@comment GNU
-@deftp {Data type} {struct __gconv_step}
-This data structure describes one conversion a module can perform. For
-each function in a loaded module with conversion functions there is
-exactly one object of this type. This object is shared by all users of
-the conversion (i.e., this object does not contain any information
-corresponding to an actual conversion; it only describes the conversion
-itself).
-
-@table @code
-@item struct __gconv_loaded_object *__shlib_handle
-@itemx const char *__modname
-@itemx int __counter
-All these elements of the structure are used internally in the C library
-to coordinate loading and unloading the shared. One must not expect any
-of the other elements to be available or initialized.
-
-@item const char *__from_name
-@itemx const char *__to_name
-@code{__from_name} and @code{__to_name} contain the names of the source and
-destination character sets. They can be used to identify the actual
-conversion to be carried out since one module might implement conversions
-for more than one character set and/or direction.
-
-@item gconv_fct __fct
-@itemx gconv_init_fct __init_fct
-@itemx gconv_end_fct __end_fct
-These elements contain pointers to the functions in the loadable module.
-The interface will be explained below.
-
-@item int __min_needed_from
-@itemx int __max_needed_from
-@itemx int __min_needed_to
-@itemx int __max_needed_to;
-These values have to be supplied in the init function of the module. The
-@code{__min_needed_from} value specifies how many bytes a character of
-the source character set at least needs. The @code{__max_needed_from}
-specifies the maximum value that also includes possible shift sequences.
-
-The @code{__min_needed_to} and @code{__max_needed_to} values serve the
-same purpose as @code{__min_needed_from} and @code{__max_needed_from} but
-this time for the destination character set.
-
-It is crucial that these values be accurate since otherwise the
-conversion functions will have problems or not work at all.
-
-@item int __stateful
-This element must also be initialized by the init function.
-@code{int __stateful} is nonzero if the source character set is stateful.
-Otherwise it is zero.
-
-@item void *__data
-This element can be used freely by the conversion functions in the
-module. @code{void *__data} can be used to communicate extra information
-from one call to another. @code{void *__data} need not be initialized if
-not needed at all. If @code{void *__data} element is assigned a pointer
-to dynamically allocated memory (presumably in the init function) it has
-to be made sure that the end function deallocates the memory. Otherwise
-the application will leak memory.
-
-It is important to be aware that this data structure is shared by all
-users of this specification conversion and therefore the @code{__data}
-element must not contain data specific to one specific use of the
-conversion function.
-@end table
-@end deftp
-
-@comment gconv.h
-@comment GNU
-@deftp {Data type} {struct __gconv_step_data}
-This is the data structure that contains the information specific to
-each use of the conversion functions.
-
-
-@table @code
-@item char *__outbuf
-@itemx char *__outbufend
-These elements specify the output buffer for the conversion step. The
-@code{__outbuf} element points to the beginning of the buffer, and
-@code{__outbufend} points to the byte following the last byte in the
-buffer. The conversion function must not assume anything about the size
-of the buffer but it can be safely assumed the there is room for at
-least one complete character in the output buffer.
-
-Once the conversion is finished, if the conversion is the last step, the
-@code{__outbuf} element must be modified to point after the last byte
-written into the buffer to signal how much output is available. If this
-conversion step is not the last one, the element must not be modified.
-The @code{__outbufend} element must not be modified.
-
-@item int __is_last
-This element is nonzero if this conversion step is the last one. This
-information is necessary for the recursion. See the description of the
-conversion function internals below. This element must never be
-modified.
-
-@item int __invocation_counter
-The conversion function can use this element to see how many calls of
-the conversion function already happened. Some character sets require a
-certain prolog when generating output, and by comparing this value with
-zero, one can find out whether it is the first call and whether,
-therefore, the prolog should be emitted. This element must never be
-modified.
-
-@item int __internal_use
-This element is another one rarely used but needed in certain
-situations. It is assigned a nonzero value in case the conversion
-functions are used to implement @code{mbsrtowcs} et.al.@: (i.e., the
-function is not used directly through the @code{iconv} interface).
-
-This sometimes makes a difference as it is expected that the
-@code{iconv} functions are used to translate entire texts while the
-@code{mbsrtowcs} functions are normally used only to convert single
-strings and might be used multiple times to convert entire texts.
-
-But in this situation we would have problem complying with some rules of
-the character set specification. Some character sets require a prolog,
-which must appear exactly once for an entire text. If a number of
-@code{mbsrtowcs} calls are used to convert the text, only the first call
-must add the prolog. However, because there is no communication between the
-different calls of @code{mbsrtowcs}, the conversion functions have no
-possibility to find this out. The situation is different for sequences
-of @code{iconv} calls since the handle allows access to the needed
-information.
-
-The @code{int __internal_use} element is mostly used together with
-@code{__invocation_counter} as follows:
-
-@smallexample
-if (!data->__internal_use
- && data->__invocation_counter == 0)
- /* @r{Emit prolog.} */
- @dots{}
-@end smallexample
-
-This element must never be modified.
-
-@item mbstate_t *__statep
-The @code{__statep} element points to an object of type @code{mbstate_t}
-(@pxref{Keeping the state}). The conversion of a stateful character
-set must use the object pointed to by @code{__statep} to store
-information about the conversion state. The @code{__statep} element
-itself must never be modified.
-
-@item mbstate_t __state
-This element must @emph{never} be used directly. It is only part of
-this structure to have the needed space allocated.
-@end table
-@end deftp
-
-@subsubsection @code{iconv} module interfaces
-
-With the knowledge about the data structures we now can describe the
-conversion function itself. To understand the interface a bit of
-knowledge is necessary about the functionality in the C library that
-loads the objects with the conversions.
-
-It is often the case that one conversion is used more than once (i.e.,
-there are several @code{iconv_open} calls for the same set of character
-sets during one program run). The @code{mbsrtowcs} et.al.@: functions in
-the GNU C library also use the @code{iconv} functionality, which
-increases the number of uses of the same functions even more.
-
-Because of this multiple use of conversions, the modules do not get
-loaded exclusively for one conversion. Instead a module once loaded can
-be used by an arbitrary number of @code{iconv} or @code{mbsrtowcs} calls
-at the same time. The splitting of the information between conversion-
-function-specific information and conversion data makes this possible.
-The last section showed the two data structures used to do this.
-
-This is of course also reflected in the interface and semantics of the
-functions that the modules must provide. There are three functions that
-must have the following names:
-
-@table @code
-@item gconv_init
-The @code{gconv_init} function initializes the conversion function
-specific data structure. This very same object is shared by all
-conversions that use this conversion and, therefore, no state information
-about the conversion itself must be stored in here. If a module
-implements more than one conversion, the @code{gconv_init} function will
-be called multiple times.
-
-@item gconv_end
-The @code{gconv_end} function is responsible for freeing all resources
-allocated by the @code{gconv_init} function. If there is nothing to do,
-this function can be missing. Special care must be taken if the module
-implements more than one conversion and the @code{gconv_init} function
-does not allocate the same resources for all conversions.
-
-@item gconv
-This is the actual conversion function. It is called to convert one
-block of text. It gets passed the conversion step information
-initialized by @code{gconv_init} and the conversion data, specific to
-this use of the conversion functions.
-@end table
-
-There are three data types defined for the three module interface
-functions and these define the interface.
-
-@comment gconv.h
-@comment GNU
-@deftypevr {Data type} int {(*__gconv_init_fct)} (struct __gconv_step *)
-This specifies the interface of the initialization function of the
-module. It is called exactly once for each conversion the module
-implements.
-
-As explained in the description of the @code{struct __gconv_step} data
-structure above the initialization function has to initialize parts of
-it.
-
-@table @code
-@item __min_needed_from
-@itemx __max_needed_from
-@itemx __min_needed_to
-@itemx __max_needed_to
-These elements must be initialized to the exact numbers of the minimum
-and maximum number of bytes used by one character in the source and
-destination character sets, respectively. If the characters all have the
-same size, the minimum and maximum values are the same.
-
-@item __stateful
-This element must be initialized to an nonzero value if the source
-character set is stateful. Otherwise it must be zero.
-@end table
-
-If the initialization function needs to communicate some information
-to the conversion function, this communication can happen using the
-@code{__data} element of the @code{__gconv_step} structure. But since
-this data is shared by all the conversions, it must not be modified by
-the conversion function. The example below shows how this can be used.
-
-@smallexample
-#define MIN_NEEDED_FROM 1
-#define MAX_NEEDED_FROM 4
-#define MIN_NEEDED_TO 4
-#define MAX_NEEDED_TO 4
-
-int
-gconv_init (struct __gconv_step *step)
-@{
- /* @r{Determine which direction.} */
- struct iso2022jp_data *new_data;
- enum direction dir = illegal_dir;
- enum variant var = illegal_var;
- int result;
-
- if (__strcasecmp (step->__from_name, "ISO-2022-JP//") == 0)
- @{
- dir = from_iso2022jp;
- var = iso2022jp;
- @}
- else if (__strcasecmp (step->__to_name, "ISO-2022-JP//") == 0)
- @{
- dir = to_iso2022jp;
- var = iso2022jp;
- @}
- else if (__strcasecmp (step->__from_name, "ISO-2022-JP-2//") == 0)
- @{
- dir = from_iso2022jp;
- var = iso2022jp2;
- @}
- else if (__strcasecmp (step->__to_name, "ISO-2022-JP-2//") == 0)
- @{
- dir = to_iso2022jp;
- var = iso2022jp2;
- @}
-
- result = __GCONV_NOCONV;
- if (dir != illegal_dir)
- @{
- new_data = (struct iso2022jp_data *)
- malloc (sizeof (struct iso2022jp_data));
-
- result = __GCONV_NOMEM;
- if (new_data != NULL)
- @{
- new_data->dir = dir;
- new_data->var = var;
- step->__data = new_data;
-
- if (dir == from_iso2022jp)
- @{
- step->__min_needed_from = MIN_NEEDED_FROM;
- step->__max_needed_from = MAX_NEEDED_FROM;
- step->__min_needed_to = MIN_NEEDED_TO;
- step->__max_needed_to = MAX_NEEDED_TO;
- @}
- else
- @{
- step->__min_needed_from = MIN_NEEDED_TO;
- step->__max_needed_from = MAX_NEEDED_TO;
- step->__min_needed_to = MIN_NEEDED_FROM;
- step->__max_needed_to = MAX_NEEDED_FROM + 2;
- @}
-
- /* @r{Yes, this is a stateful encoding.} */
- step->__stateful = 1;
-
- result = __GCONV_OK;
- @}
- @}
-
- return result;
-@}
-@end smallexample
-
-The function first checks which conversion is wanted. The module from
-which this function is taken implements four different conversions;
-which one is selected can be determined by comparing the names. The
-comparison should always be done without paying attention to the case.
-
-Next, a data structure, which contains the necessary information about
-which conversion is selected, is allocated. The data structure
-@code{struct iso2022jp_data} is locally defined since, outside the
-module, this data is not used at all. Please note that if all four
-conversions this modules supports are requested there are four data
-blocks.
-
-One interesting thing is the initialization of the @code{__min_} and
-@code{__max_} elements of the step data object. A single ISO-2022-JP
-character can consist of one to four bytes. Therefore the
-@code{MIN_NEEDED_FROM} and @code{MAX_NEEDED_FROM} macros are defined
-this way. The output is always the @code{INTERNAL} character set (aka
-UCS-4) and therefore each character consists of exactly four bytes. For
-the conversion from @code{INTERNAL} to ISO-2022-JP we have to take into
-account that escape sequences might be necessary to switch the character
-sets. Therefore the @code{__max_needed_to} element for this direction
-gets assigned @code{MAX_NEEDED_FROM + 2}. This takes into account the
-two bytes needed for the escape sequences to single the switching. The
-asymmetry in the maximum values for the two directions can be explained
-easily: when reading ISO-2022-JP text, escape sequences can be handled
-alone (i.e., it is not necessary to process a real character since the
-effect of the escape sequence can be recorded in the state information).
-The situation is different for the other direction. Since it is in
-general not known which character comes next, one cannot emit escape
-sequences to change the state in advance. This means the escape
-sequences that have to be emitted together with the next character.
-Therefore one needs more room than only for the character itself.
-
-The possible return values of the initialization function are:
-
-@table @code
-@item __GCONV_OK
-The initialization succeeded
-@item __GCONV_NOCONV
-The requested conversion is not supported in the module. This can
-happen if the @file{gconv-modules} file has errors.
-@item __GCONV_NOMEM
-Memory required to store additional information could not be allocated.
-@end table
-@end deftypevr
-
-The function called before the module is unloaded is significantly
-easier. It often has nothing at all to do; in which case it can be left
-out completely.
-
-@comment gconv.h
-@comment GNU
-@deftypevr {Data type} void {(*__gconv_end_fct)} (struct gconv_step *)
-The task of this function is to free all resources allocated in the
-initialization function. Therefore only the @code{__data} element of
-the object pointed to by the argument is of interest. Continuing the
-example from the initialization function, the finalization function
-looks like this:
-
-@smallexample
-void
-gconv_end (struct __gconv_step *data)
-@{
- free (data->__data);
-@}
-@end smallexample
-@end deftypevr
-
-The most important function is the conversion function itself, which can
-get quite complicated for complex character sets. But since this is not
-of interest here, we will only describe a possible skeleton for the
-conversion function.
-
-@comment gconv.h
-@comment GNU
-@deftypevr {Data type} int {(*__gconv_fct)} (struct __gconv_step *, struct __gconv_step_data *, const char **, const char *, size_t *, int)
-The conversion function can be called for two basic reason: to convert
-text or to reset the state. From the description of the @code{iconv}
-function it can be seen why the flushing mode is necessary. What mode
-is selected is determined by the sixth argument, an integer. This
-argument being nonzero means that flushing is selected.
-
-Common to both modes is where the output buffer can be found. The
-information about this buffer is stored in the conversion step data. A
-pointer to this information is passed as the second argument to this
-function. The description of the @code{struct __gconv_step_data}
-structure has more information on the conversion step data.
-
-@cindex stateful
-What has to be done for flushing depends on the source character set.
-If the source character set is not stateful, nothing has to be done.
-Otherwise the function has to emit a byte sequence to bring the state
-object into the initial state. Once this all happened the other
-conversion modules in the chain of conversions have to get the same
-chance. Whether another step follows can be determined from the
-@code{__is_last} element of the step data structure to which the first
-parameter points.
-
-The more interesting mode is when actual text has to be converted. The
-first step in this case is to convert as much text as possible from the
-input buffer and store the result in the output buffer. The start of the
-input buffer is determined by the third argument, which is a pointer to a
-pointer variable referencing the beginning of the buffer. The fourth
-argument is a pointer to the byte right after the last byte in the buffer.
-
-The conversion has to be performed according to the current state if the
-character set is stateful. The state is stored in an object pointed to
-by the @code{__statep} element of the step data (second argument). Once
-either the input buffer is empty or the output buffer is full the
-conversion stops. At this point, the pointer variable referenced by the
-third parameter must point to the byte following the last processed
-byte (i.e., if all of the input is consumed, this pointer and the fourth
-parameter have the same value).
-
-What now happens depends on whether this step is the last one. If it is
-the last step, the only thing that has to be done is to update the
-@code{__outbuf} element of the step data structure to point after the
-last written byte. This update gives the caller the information on how
-much text is available in the output buffer. In addition, the variable
-pointed to by the fifth parameter, which is of type @code{size_t}, must
-be incremented by the number of characters (@emph{not bytes}) that were
-converted in a non-reversible way. Then, the function can return.
-
-In case the step is not the last one, the later conversion functions have
-to get a chance to do their work. Therefore, the appropriate conversion
-function has to be called. The information about the functions is
-stored in the conversion data structures, passed as the first parameter.
-This information and the step data are stored in arrays, so the next
-element in both cases can be found by simple pointer arithmetic:
-
-@smallexample
-int
-gconv (struct __gconv_step *step, struct __gconv_step_data *data,
- const char **inbuf, const char *inbufend, size_t *written,
- int do_flush)
-@{
- struct __gconv_step *next_step = step + 1;
- struct __gconv_step_data *next_data = data + 1;
- @dots{}
-@end smallexample
-
-The @code{next_step} pointer references the next step information and
-@code{next_data} the next data record. The call of the next function
-therefore will look similar to this:
-
-@smallexample
- next_step->__fct (next_step, next_data, &outerr, outbuf,
- written, 0)
-@end smallexample
-
-But this is not yet all. Once the function call returns the conversion
-function might have some more to do. If the return value of the function
-is @code{__GCONV_EMPTY_INPUT}, more room is available in the output
-buffer. Unless the input buffer is empty the conversion, functions start
-all over again and process the rest of the input buffer. If the return
-value is not @code{__GCONV_EMPTY_INPUT}, something went wrong and we have
-to recover from this.
-
-A requirement for the conversion function is that the input buffer
-pointer (the third argument) always point to the last character that
-was put in converted form into the output buffer. This is trivially
-true after the conversion performed in the current step, but if the
-conversion functions deeper downstream stop prematurely, not all
-characters from the output buffer are consumed and, therefore, the input
-buffer pointers must be backed off to the right position.
-
-Correcting the input buffers is easy to do if the input and output
-character sets have a fixed width for all characters. In this situation
-we can compute how many characters are left in the output buffer and,
-therefore, can correct the input buffer pointer appropriately with a
-similar computation. Things are getting tricky if either character set
-has characters represented with variable length byte sequences, and it
-gets even more complicated if the conversion has to take care of the
-state. In these cases the conversion has to be performed once again, from
-the known state before the initial conversion (i.e., if necessary the
-state of the conversion has to be reset and the conversion loop has to be
-executed again). The difference now is that it is known how much input
-must be created, and the conversion can stop before converting the first
-unused character. Once this is done the input buffer pointers must be
-updated again and the function can return.
-
-One final thing should be mentioned. If it is necessary for the
-conversion to know whether it is the first invocation (in case a prolog
-has to be emitted), the conversion function should increment the
-@code{__invocation_counter} element of the step data structure just
-before returning to the caller. See the description of the @code{struct
-__gconv_step_data} structure above for more information on how this can
-be used.
-
-The return value must be one of the following values:
-
-@table @code
-@item __GCONV_EMPTY_INPUT
-All input was consumed and there is room left in the output buffer.
-@item __GCONV_FULL_OUTPUT
-No more room in the output buffer. In case this is not the last step
-this value is propagated down from the call of the next conversion
-function in the chain.
-@item __GCONV_INCOMPLETE_INPUT
-The input buffer is not entirely empty since it contains an incomplete
-character sequence.
-@end table
-
-The following example provides a framework for a conversion function.
-In case a new conversion has to be written the holes in this
-implementation have to be filled and that is it.
-
-@smallexample
-int
-gconv (struct __gconv_step *step, struct __gconv_step_data *data,
- const char **inbuf, const char *inbufend, size_t *written,
- int do_flush)
-@{
- struct __gconv_step *next_step = step + 1;
- struct __gconv_step_data *next_data = data + 1;
- gconv_fct fct = next_step->__fct;
- int status;
-
- /* @r{If the function is called with no input this means we have}
- @r{to reset to the initial state. The possibly partly}
- @r{converted input is dropped.} */
- if (do_flush)
- @{
- status = __GCONV_OK;
-
- /* @r{Possible emit a byte sequence which put the state object}
- @r{into the initial state.} */
-
- /* @r{Call the steps down the chain if there are any but only}
- @r{if we successfully emitted the escape sequence.} */
- if (status == __GCONV_OK && ! data->__is_last)
- status = fct (next_step, next_data, NULL, NULL,
- written, 1);
- @}
- else
- @{
- /* @r{We preserve the initial values of the pointer variables.} */
- const char *inptr = *inbuf;
- char *outbuf = data->__outbuf;
- char *outend = data->__outbufend;
- char *outptr;
-
- do
- @{
- /* @r{Remember the start value for this round.} */
- inptr = *inbuf;
- /* @r{The outbuf buffer is empty.} */
- outptr = outbuf;
-
- /* @r{For stateful encodings the state must be safe here.} */
-
- /* @r{Run the conversion loop. @code{status} is set}
- @r{appropriately afterwards.} */
-
- /* @r{If this is the last step, leave the loop. There is}
- @r{nothing we can do.} */
- if (data->__is_last)
- @{
- /* @r{Store information about how many bytes are}
- @r{available.} */
- data->__outbuf = outbuf;
-
- /* @r{If any non-reversible conversions were performed,}
- @r{add the number to @code{*written}.} */
-
- break;
- @}
-
- /* @r{Write out all output that was produced.} */
- if (outbuf > outptr)
- @{
- const char *outerr = data->__outbuf;
- int result;
-
- result = fct (next_step, next_data, &outerr,
- outbuf, written, 0);
-
- if (result != __GCONV_EMPTY_INPUT)
- @{
- if (outerr != outbuf)
- @{
- /* @r{Reset the input buffer pointer. We}
- @r{document here the complex case.} */
- size_t nstatus;
-
- /* @r{Reload the pointers.} */
- *inbuf = inptr;
- outbuf = outptr;
-
- /* @r{Possibly reset the state.} */
-
- /* @r{Redo the conversion, but this time}
- @r{the end of the output buffer is at}
- @r{@code{outerr}.} */
- @}
-
- /* @r{Change the status.} */
- status = result;
- @}
- else
- /* @r{All the output is consumed, we can make}
- @r{ another run if everything was ok.} */
- if (status == __GCONV_FULL_OUTPUT)
- status = __GCONV_OK;
- @}
- @}
- while (status == __GCONV_OK);
-
- /* @r{We finished one use of this step.} */
- ++data->__invocation_counter;
- @}
-
- return status;
-@}
-@end smallexample
-@end deftypevr
-
-This information should be sufficient to write new modules. Anybody
-doing so should also take a look at the available source code in the GNU
-C library sources. It contains many examples of working and optimized
-modules.
-
-@c File charset.texi edited October 2001 by Dennis Grace, IBM Corporation
Copied: glibc-doc-reference/tags/2.13-1/manual/charset.texi (from rev 4338, glibc-doc-reference/trunk/manual/charset.texi)
===================================================================
--- glibc-doc-reference/tags/2.13-1/manual/charset.texi (rev 0)
+++ glibc-doc-reference/tags/2.13-1/manual/charset.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,2895 @@
+@node Character Set Handling, Locales, String and Array Utilities, Top
+@c %MENU% Support for extended character sets
+@chapter Character Set Handling
+
+@ifnottex
+@macro cal{text}
+\text\
+@end macro
+@end ifnottex
+
+Character sets used in the early days of computing had only six, seven,
+or eight bits for each character: there was never a case where more than
+eight bits (one byte) were used to represent a single character. The
+limitations of this approach became more apparent as more people
+grappled with non-Roman character sets, where not all the characters
+that make up a language's character set can be represented by @math{2^8}
+choices. This chapter shows the functionality that was added to the C
+library to support multiple character sets.
+
+@menu
+* Extended Char Intro:: Introduction to Extended Characters.
+* Charset Function Overview:: Overview about Character Handling
+ Functions.
+* Restartable multibyte conversion:: Restartable multibyte conversion
+ Functions.
+* Non-reentrant Conversion:: Non-reentrant Conversion Function.
+* Generic Charset Conversion:: Generic Charset Conversion.
+@end menu
+
+
+@node Extended Char Intro
+@section Introduction to Extended Characters
+
+A variety of solutions is available to overcome the differences between
+character sets with a 1:1 relation between bytes and characters and
+character sets with ratios of 2:1 or 4:1. The remainder of this
+section gives a few examples to help understand the design decisions
+made while developing the functionality of the @w{C library}.
+
+@cindex internal representation
+A distinction we have to make right away is between internal and
+external representation. @dfn{Internal representation} means the
+representation used by a program while keeping the text in memory.
+External representations are used when text is stored or transmitted
+through some communication channel. Examples of external
+representations include files waiting in a directory to be
+read and parsed.
+
+Traditionally there has been no difference between the two representations.
+It was equally comfortable and useful to use the same single-byte
+representation internally and externally. This comfort level decreases
+with more and larger character sets.
+
+One of the problems to overcome with the internal representation is
+handling text that is externally encoded using different character
+sets. Assume a program that reads two texts and compares them using
+some metric. The comparison can be usefully done only if the texts are
+internally kept in a common format.
+
+@cindex wide character
+For such a common format (@math{=} character set) eight bits are certainly
+no longer enough. So the smallest entity will have to grow: @dfn{wide
+characters} will now be used. Instead of one byte per character, two or
+four will be used instead. (Three are not good to address in memory and
+more than four bytes seem not to be necessary).
+
+@cindex Unicode
+@cindex ISO 10646
+As shown in some other part of this manual,
+@c !!! Ahem, wide char string functions are not yet covered -- drepper
+a completely new family has been created of functions that can handle wide
+character texts in memory. The most commonly used character sets for such
+internal wide character representations are Unicode and @w{ISO 10646}
+(also known as UCS for Universal Character Set). Unicode was originally
+planned as a 16-bit character set; whereas, @w{ISO 10646} was designed to
+be a 31-bit large code space. The two standards are practically identical.
+They have the same character repertoire and code table, but Unicode specifies
+added semantics. At the moment, only characters in the first @code{0x10000}
+code positions (the so-called Basic Multilingual Plane, BMP) have been
+assigned, but the assignment of more specialized characters outside this
+16-bit space is already in progress. A number of encodings have been
+defined for Unicode and @w{ISO 10646} characters:
+@cindex UCS-2
+@cindex UCS-4
+@cindex UTF-8
+@cindex UTF-16
+UCS-2 is a 16-bit word that can only represent characters
+from the BMP, UCS-4 is a 32-bit word than can represent any Unicode
+and @w{ISO 10646} character, UTF-8 is an ASCII compatible encoding where
+ASCII characters are represented by ASCII bytes and non-ASCII characters
+by sequences of 2-6 non-ASCII bytes, and finally UTF-16 is an extension
+of UCS-2 in which pairs of certain UCS-2 words can be used to encode
+non-BMP characters up to @code{0x10ffff}.
+
+To represent wide characters the @code{char} type is not suitable. For
+this reason the @w{ISO C} standard introduces a new type that is
+designed to keep one character of a wide character string. To maintain
+the similarity there is also a type corresponding to @code{int} for
+those functions that take a single wide character.
+
+@comment stddef.h
+@comment ISO
+@deftp {Data type} wchar_t
+This data type is used as the base type for wide character strings.
+In other words, arrays of objects of this type are the equivalent of
+@code{char[]} for multibyte character strings. The type is defined in
+@file{stddef.h}.
+
+The @w{ISO C90} standard, where @code{wchar_t} was introduced, does not
+say anything specific about the representation. It only requires that
+this type is capable of storing all elements of the basic character set.
+Therefore it would be legitimate to define @code{wchar_t} as @code{char},
+which might make sense for embedded systems.
+
+But for GNU systems @code{wchar_t} is always 32 bits wide and, therefore,
+capable of representing all UCS-4 values and, therefore, covering all of
+@w{ISO 10646}. Some Unix systems define @code{wchar_t} as a 16-bit type
+and thereby follow Unicode very strictly. This definition is perfectly
+fine with the standard, but it also means that to represent all
+characters from Unicode and @w{ISO 10646} one has to use UTF-16 surrogate
+characters, which is in fact a multi-wide-character encoding. But
+resorting to multi-wide-character encoding contradicts the purpose of the
+@code{wchar_t} type.
+@end deftp
+
+@comment wchar.h
+@comment ISO
+@deftp {Data type} wint_t
+@code{wint_t} is a data type used for parameters and variables that
+contain a single wide character. As the name suggests this type is the
+equivalent of @code{int} when using the normal @code{char} strings. The
+types @code{wchar_t} and @code{wint_t} often have the same
+representation if their size is 32 bits wide but if @code{wchar_t} is
+defined as @code{char} the type @code{wint_t} must be defined as
+@code{int} due to the parameter promotion.
+
+@pindex wchar.h
+This type is defined in @file{wchar.h} and was introduced in
+@w{Amendment 1} to @w{ISO C90}.
+@end deftp
+
+As there are for the @code{char} data type macros are available for
+specifying the minimum and maximum value representable in an object of
+type @code{wchar_t}.
+
+@comment wchar.h
+@comment ISO
+@deftypevr Macro wint_t WCHAR_MIN
+The macro @code{WCHAR_MIN} evaluates to the minimum value representable
+by an object of type @code{wint_t}.
+
+This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
+@end deftypevr
+
+@comment wchar.h
+@comment ISO
+@deftypevr Macro wint_t WCHAR_MAX
+The macro @code{WCHAR_MAX} evaluates to the maximum value representable
+by an object of type @code{wint_t}.
+
+This macro was introduced in @w{Amendment 1} to @w{ISO C90}.
+@end deftypevr
+
+Another special wide character value is the equivalent to @code{EOF}.
+
+@comment wchar.h
+@comment ISO
+@deftypevr Macro wint_t WEOF
+The macro @code{WEOF} evaluates to a constant expression of type
+@code{wint_t} whose value is different from any member of the extended
+character set.
+
+@code{WEOF} need not be the same value as @code{EOF} and unlike
+@code{EOF} it also need @emph{not} be negative. In other words, sloppy
+code like
+
+@smallexample
+@{
+ int c;
+ @dots{}
+ while ((c = getc (fp)) < 0)
+ @dots{}
+@}
+@end smallexample
+
+@noindent
+has to be rewritten to use @code{WEOF} explicitly when wide characters
+are used:
+
+@smallexample
+@{
+ wint_t c;
+ @dots{}
+ while ((c = wgetc (fp)) != WEOF)
+ @dots{}
+@}
+@end smallexample
+
+@pindex wchar.h
+This macro was introduced in @w{Amendment 1} to @w{ISO C90} and is
+defined in @file{wchar.h}.
+@end deftypevr
+
+
+These internal representations present problems when it comes to storing
+and transmittal. Because each single wide character consists of more
+than one byte, they are effected by byte-ordering. Thus, machines with
+different endianesses would see different values when accessing the same
+data. This byte ordering concern also applies for communication protocols
+that are all byte-based and therefore require that the sender has to
+decide about splitting the wide character in bytes. A last (but not least
+important) point is that wide characters often require more storage space
+than a customized byte-oriented character set.
+
+@cindex multibyte character
+@cindex EBCDIC
+For all the above reasons, an external encoding that is different from
+the internal encoding is often used if the latter is UCS-2 or UCS-4.
+The external encoding is byte-based and can be chosen appropriately for
+the environment and for the texts to be handled. A variety of different
+character sets can be used for this external encoding (information that
+will not be exhaustively presented here--instead, a description of the
+major groups will suffice). All of the ASCII-based character sets
+fulfill one requirement: they are "filesystem safe." This means that
+the character @code{'/'} is used in the encoding @emph{only} to
+represent itself. Things are a bit different for character sets like
+EBCDIC (Extended Binary Coded Decimal Interchange Code, a character set
+family used by IBM), but if the operation system does not understand
+EBCDIC directly the parameters-to-system calls have to be converted
+first anyhow.
+
+@itemize @bullet
+@item
+The simplest character sets are single-byte character sets. There can
+be only up to 256 characters (for @w{8 bit} character sets), which is
+not sufficient to cover all languages but might be sufficient to handle
+a specific text. Handling of a @w{8 bit} character sets is simple. This
+is not true for other kinds presented later, and therefore, the
+application one uses might require the use of @w{8 bit} character sets.
+
+@cindex ISO 2022
+@item
+The @w{ISO 2022} standard defines a mechanism for extended character
+sets where one character @emph{can} be represented by more than one
+byte. This is achieved by associating a state with the text.
+Characters that can be used to change the state can be embedded in the
+text. Each byte in the text might have a different interpretation in each
+state. The state might even influence whether a given byte stands for a
+character on its own or whether it has to be combined with some more
+bytes.
+
+@cindex EUC
+@cindex Shift_JIS
+@cindex SJIS
+In most uses of @w{ISO 2022} the defined character sets do not allow
+state changes that cover more than the next character. This has the
+big advantage that whenever one can identify the beginning of the byte
+sequence of a character one can interpret a text correctly. Examples of
+character sets using this policy are the various EUC character sets
+(used by Sun's operations systems, EUC-JP, EUC-KR, EUC-TW, and EUC-CN)
+or Shift_JIS (SJIS, a Japanese encoding).
+
+But there are also character sets using a state that is valid for more
+than one character and has to be changed by another byte sequence.
+Examples for this are ISO-2022-JP, ISO-2022-KR, and ISO-2022-CN.
+
+@item
+@cindex ISO 6937
+Early attempts to fix 8 bit character sets for other languages using the
+Roman alphabet lead to character sets like @w{ISO 6937}. Here bytes
+representing characters like the acute accent do not produce output
+themselves: one has to combine them with other characters to get the
+desired result. For example, the byte sequence @code{0xc2 0x61}
+(non-spacing acute accent, followed by lower-case `a') to get the ``small
+a with acute'' character. To get the acute accent character on its own,
+one has to write @code{0xc2 0x20} (the non-spacing acute followed by a
+space).
+
+Character sets like @w{ISO 6937} are used in some embedded systems such
+as teletex.
+
+@item
+@cindex UTF-8
+Instead of converting the Unicode or @w{ISO 10646} text used internally,
+it is often also sufficient to simply use an encoding different than
+UCS-2/UCS-4. The Unicode and @w{ISO 10646} standards even specify such an
+encoding: UTF-8. This encoding is able to represent all of @w{ISO
+10646} 31 bits in a byte string of length one to six.
+
+@cindex UTF-7
+There were a few other attempts to encode @w{ISO 10646} such as UTF-7,
+but UTF-8 is today the only encoding that should be used. In fact, with
+any luck UTF-8 will soon be the only external encoding that has to be
+supported. It proves to be universally usable and its only disadvantage
+is that it favors Roman languages by making the byte string
+representation of other scripts (Cyrillic, Greek, Asian scripts) longer
+than necessary if using a specific character set for these scripts.
+Methods like the Unicode compression scheme can alleviate these
+problems.
+@end itemize
+
+The question remaining is: how to select the character set or encoding
+to use. The answer: you cannot decide about it yourself, it is decided
+by the developers of the system or the majority of the users. Since the
+goal is interoperability one has to use whatever the other people one
+works with use. If there are no constraints, the selection is based on
+the requirements the expected circle of users will have. In other words,
+if a project is expected to be used in only, say, Russia it is fine to use
+KOI8-R or a similar character set. But if at the same time people from,
+say, Greece are participating one should use a character set that allows
+all people to collaborate.
+
+The most widely useful solution seems to be: go with the most general
+character set, namely @w{ISO 10646}. Use UTF-8 as the external encoding
+and problems about users not being able to use their own language
+adequately are a thing of the past.
+
+One final comment about the choice of the wide character representation
+is necessary at this point. We have said above that the natural choice
+is using Unicode or @w{ISO 10646}. This is not required, but at least
+encouraged, by the @w{ISO C} standard. The standard defines at least a
+macro @code{__STDC_ISO_10646__} that is only defined on systems where
+the @code{wchar_t} type encodes @w{ISO 10646} characters. If this
+symbol is not defined one should avoid making assumptions about the wide
+character representation. If the programmer uses only the functions
+provided by the C library to handle wide character strings there should
+be no compatibility problems with other systems.
+
+@node Charset Function Overview
+@section Overview about Character Handling Functions
+
+A Unix @w{C library} contains three different sets of functions in two
+families to handle character set conversion. One of the function families
+(the most commonly used) is specified in the @w{ISO C90} standard and,
+therefore, is portable even beyond the Unix world. Unfortunately this
+family is the least useful one. These functions should be avoided
+whenever possible, especially when developing libraries (as opposed to
+applications).
+
+The second family of functions got introduced in the early Unix standards
+(XPG2) and is still part of the latest and greatest Unix standard:
+@w{Unix 98}. It is also the most powerful and useful set of functions.
+But we will start with the functions defined in @w{Amendment 1} to
+@w{ISO C90}.
+
+@node Restartable multibyte conversion
+@section Restartable Multibyte Conversion Functions
+
+The @w{ISO C} standard defines functions to convert strings from a
+multibyte representation to wide character strings. There are a number
+of peculiarities:
+
+@itemize @bullet
+@item
+The character set assumed for the multibyte encoding is not specified
+as an argument to the functions. Instead the character set specified by
+the @code{LC_CTYPE} category of the current locale is used; see
+@ref{Locale Categories}.
+
+@item
+The functions handling more than one character at a time require NUL
+terminated strings as the argument (i.e., converting blocks of text
+does not work unless one can add a NUL byte at an appropriate place).
+The GNU C library contains some extensions to the standard that allow
+specifying a size, but basically they also expect terminated strings.
+@end itemize
+
+Despite these limitations the @w{ISO C} functions can be used in many
+contexts. In graphical user interfaces, for instance, it is not
+uncommon to have functions that require text to be displayed in a wide
+character string if the text is not simple ASCII. The text itself might
+come from a file with translations and the user should decide about the
+current locale, which determines the translation and therefore also the
+external encoding used. In such a situation (and many others) the
+functions described here are perfect. If more freedom while performing
+the conversion is necessary take a look at the @code{iconv} functions
+(@pxref{Generic Charset Conversion}).
+
+@menu
+* Selecting the Conversion:: Selecting the conversion and its properties.
+* Keeping the state:: Representing the state of the conversion.
+* Converting a Character:: Converting Single Characters.
+* Converting Strings:: Converting Multibyte and Wide Character
+ Strings.
+* Multibyte Conversion Example:: A Complete Multibyte Conversion Example.
+@end menu
+
+@node Selecting the Conversion
+@subsection Selecting the conversion and its properties
+
+We already said above that the currently selected locale for the
+@code{LC_CTYPE} category decides about the conversion that is performed
+by the functions we are about to describe. Each locale uses its own
+character set (given as an argument to @code{localedef}) and this is the
+one assumed as the external multibyte encoding. The wide character
+set is always UCS-4, at least on GNU systems.
+
+A characteristic of each multibyte character set is the maximum number
+of bytes that can be necessary to represent one character. This
+information is quite important when writing code that uses the
+conversion functions (as shown in the examples below).
+The @w{ISO C} standard defines two macros that provide this information.
+
+
+@comment limits.h
+@comment ISO
+@deftypevr Macro int MB_LEN_MAX
+@code{MB_LEN_MAX} specifies the maximum number of bytes in the multibyte
+sequence for a single character in any of the supported locales. It is
+a compile-time constant and is defined in @file{limits.h}.
+@pindex limits.h
+@end deftypevr
+
+@comment stdlib.h
+@comment ISO
+@deftypevr Macro int MB_CUR_MAX
+@code{MB_CUR_MAX} expands into a positive integer expression that is the
+maximum number of bytes in a multibyte character in the current locale.
+The value is never greater than @code{MB_LEN_MAX}. Unlike
+@code{MB_LEN_MAX} this macro need not be a compile-time constant, and in
+the GNU C library it is not.
+
+@pindex stdlib.h
+@code{MB_CUR_MAX} is defined in @file{stdlib.h}.
+@end deftypevr
+
+Two different macros are necessary since strictly @w{ISO C90} compilers
+do not allow variable length array definitions, but still it is desirable
+to avoid dynamic allocation. This incomplete piece of code shows the
+problem:
+
+@smallexample
+@{
+ char buf[MB_LEN_MAX];
+ ssize_t len = 0;
+
+ while (! feof (fp))
+ @{
+ fread (&buf[len], 1, MB_CUR_MAX - len, fp);
+ /* @r{@dots{} process} buf */
+ len -= used;
+ @}
+@}
+@end smallexample
+
+The code in the inner loop is expected to have always enough bytes in
+the array @var{buf} to convert one multibyte character. The array
+@var{buf} has to be sized statically since many compilers do not allow a
+variable size. The @code{fread} call makes sure that @code{MB_CUR_MAX}
+bytes are always available in @var{buf}. Note that it isn't
+a problem if @code{MB_CUR_MAX} is not a compile-time constant.
+
+
+@node Keeping the state
+@subsection Representing the state of the conversion
+
+@cindex stateful
+In the introduction of this chapter it was said that certain character
+sets use a @dfn{stateful} encoding. That is, the encoded values depend
+in some way on the previous bytes in the text.
+
+Since the conversion functions allow converting a text in more than one
+step we must have a way to pass this information from one call of the
+functions to another.
+
+@comment wchar.h
+@comment ISO
+@deftp {Data type} mbstate_t
+@cindex shift state
+A variable of type @code{mbstate_t} can contain all the information
+about the @dfn{shift state} needed from one call to a conversion
+function to another.
+
+@pindex wchar.h
+@code{mbstate_t} is defined in @file{wchar.h}. It was introduced in
+@w{Amendment 1} to @w{ISO C90}.
+@end deftp
+
+To use objects of type @code{mbstate_t} the programmer has to define such
+objects (normally as local variables on the stack) and pass a pointer to
+the object to the conversion functions. This way the conversion function
+can update the object if the current multibyte character set is stateful.
+
+There is no specific function or initializer to put the state object in
+any specific state. The rules are that the object should always
+represent the initial state before the first use, and this is achieved by
+clearing the whole variable with code such as follows:
+
+@smallexample
+@{
+ mbstate_t state;
+ memset (&state, '\0', sizeof (state));
+ /* @r{from now on @var{state} can be used.} */
+ @dots{}
+@}
+@end smallexample
+
+When using the conversion functions to generate output it is often
+necessary to test whether the current state corresponds to the initial
+state. This is necessary, for example, to decide whether to emit
+escape sequences to set the state to the initial state at certain
+sequence points. Communication protocols often require this.
+
+@comment wchar.h
+@comment ISO
+@deftypefun int mbsinit (const mbstate_t *@var{ps})
+The @code{mbsinit} function determines whether the state object pointed
+to by @var{ps} is in the initial state. If @var{ps} is a null pointer or
+the object is in the initial state the return value is nonzero. Otherwise
+it is zero.
+
+@pindex wchar.h
+@code{mbsinit} was introduced in @w{Amendment 1} to @w{ISO C90} and is
+declared in @file{wchar.h}.
+@end deftypefun
+
+Code using @code{mbsinit} often looks similar to this:
+
+@c Fix the example to explicitly say how to generate the escape sequence
+@c to restore the initial state.
+@smallexample
+@{
+ mbstate_t state;
+ memset (&state, '\0', sizeof (state));
+ /* @r{Use @var{state}.} */
+ @dots{}
+ if (! mbsinit (&state))
+ @{
+ /* @r{Emit code to return to initial state.} */
+ const wchar_t empty[] = L"";
+ const wchar_t *srcp = empty;
+ wcsrtombs (outbuf, &srcp, outbuflen, &state);
+ @}
+ @dots{}
+@}
+@end smallexample
+
+The code to emit the escape sequence to get back to the initial state is
+interesting. The @code{wcsrtombs} function can be used to determine the
+necessary output code (@pxref{Converting Strings}). Please note that on
+GNU systems it is not necessary to perform this extra action for the
+conversion from multibyte text to wide character text since the wide
+character encoding is not stateful. But there is nothing mentioned in
+any standard that prohibits making @code{wchar_t} using a stateful
+encoding.
+
+@node Converting a Character
+@subsection Converting Single Characters
+
+The most fundamental of the conversion functions are those dealing with
+single characters. Please note that this does not always mean single
+bytes. But since there is very often a subset of the multibyte
+character set that consists of single byte sequences, there are
+functions to help with converting bytes. Frequently, ASCII is a subpart
+of the multibyte character set. In such a scenario, each ASCII character
+stands for itself, and all other characters have at least a first byte
+that is beyond the range @math{0} to @math{127}.
+
+@comment wchar.h
+@comment ISO
+@deftypefun wint_t btowc (int @var{c})
+The @code{btowc} function (``byte to wide character'') converts a valid
+single byte character @var{c} in the initial shift state into the wide
+character equivalent using the conversion rules from the currently
+selected locale of the @code{LC_CTYPE} category.
+
+If @code{(unsigned char) @var{c}} is no valid single byte multibyte
+character or if @var{c} is @code{EOF}, the function returns @code{WEOF}.
+
+Please note the restriction of @var{c} being tested for validity only in
+the initial shift state. No @code{mbstate_t} object is used from
+which the state information is taken, and the function also does not use
+any static state.
+
+@pindex wchar.h
+The @code{btowc} function was introduced in @w{Amendment 1} to @w{ISO C90}
+and is declared in @file{wchar.h}.
+@end deftypefun
+
+Despite the limitation that the single byte value is always interpreted
+in the initial state, this function is actually useful most of the time.
+Most characters are either entirely single-byte character sets or they
+are extension to ASCII. But then it is possible to write code like this
+(not that this specific example is very useful):
+
+@smallexample
+wchar_t *
+itow (unsigned long int val)
+@{
+ static wchar_t buf[30];
+ wchar_t *wcp = &buf[29];
+ *wcp = L'\0';
+ while (val != 0)
+ @{
+ *--wcp = btowc ('0' + val % 10);
+ val /= 10;
+ @}
+ if (wcp == &buf[29])
+ *--wcp = L'0';
+ return wcp;
+@}
+@end smallexample
+
+Why is it necessary to use such a complicated implementation and not
+simply cast @code{'0' + val % 10} to a wide character? The answer is
+that there is no guarantee that one can perform this kind of arithmetic
+on the character of the character set used for @code{wchar_t}
+representation. In other situations the bytes are not constant at
+compile time and so the compiler cannot do the work. In situations like
+this, using @code{btowc} is required.
+
+@noindent
+There is also a function for the conversion in the other direction.
+
+@comment wchar.h
+@comment ISO
+@deftypefun int wctob (wint_t @var{c})
+The @code{wctob} function (``wide character to byte'') takes as the
+parameter a valid wide character. If the multibyte representation for
+this character in the initial state is exactly one byte long, the return
+value of this function is this character. Otherwise the return value is
+@code{EOF}.
+
+@pindex wchar.h
+@code{wctob} was introduced in @w{Amendment 1} to @w{ISO C90} and
+is declared in @file{wchar.h}.
+@end deftypefun
+
+There are more general functions to convert single character from
+multibyte representation to wide characters and vice versa. These
+functions pose no limit on the length of the multibyte representation
+and they also do not require it to be in the initial state.
+
+@comment wchar.h
+@comment ISO
+@deftypefun size_t mbrtowc (wchar_t *restrict @var{pwc}, const char *restrict @var{s}, size_t @var{n}, mbstate_t *restrict @var{ps})
+@cindex stateful
+The @code{mbrtowc} function (``multibyte restartable to wide
+character'') converts the next multibyte character in the string pointed
+to by @var{s} into a wide character and stores it in the wide character
+string pointed to by @var{pwc}. The conversion is performed according
+to the locale currently selected for the @code{LC_CTYPE} category. If
+the conversion for the character set used in the locale requires a state,
+the multibyte string is interpreted in the state represented by the
+object pointed to by @var{ps}. If @var{ps} is a null pointer, a static,
+internal state variable used only by the @code{mbrtowc} function is
+used.
+
+If the next multibyte character corresponds to the NUL wide character,
+the return value of the function is @math{0} and the state object is
+afterwards in the initial state. If the next @var{n} or fewer bytes
+form a correct multibyte character, the return value is the number of
+bytes starting from @var{s} that form the multibyte character. The
+conversion state is updated according to the bytes consumed in the
+conversion. In both cases the wide character (either the @code{L'\0'}
+or the one found in the conversion) is stored in the string pointed to
+by @var{pwc} if @var{pwc} is not null.
+
+If the first @var{n} bytes of the multibyte string possibly form a valid
+multibyte character but there are more than @var{n} bytes needed to
+complete it, the return value of the function is @code{(size_t) -2} and
+no value is stored. Please note that this can happen even if @var{n}
+has a value greater than or equal to @code{MB_CUR_MAX} since the input
+might contain redundant shift sequences.
+
+If the first @code{n} bytes of the multibyte string cannot possibly form
+a valid multibyte character, no value is stored, the global variable
+@code{errno} is set to the value @code{EILSEQ}, and the function returns
+@code{(size_t) -1}. The conversion state is afterwards undefined.
+
+@pindex wchar.h
+@code{mbrtowc} was introduced in @w{Amendment 1} to @w{ISO C90} and
+is declared in @file{wchar.h}.
+@end deftypefun
+
+Use of @code{mbrtowc} is straightforward. A function that copies a
+multibyte string into a wide character string while at the same time
+converting all lowercase characters into uppercase could look like this
+(this is not the final version, just an example; it has no error
+checking, and sometimes leaks memory):
+
+@smallexample
+wchar_t *
+mbstouwcs (const char *s)
+@{
+ size_t len = strlen (s);
+ wchar_t *result = malloc ((len + 1) * sizeof (wchar_t));
+ wchar_t *wcp = result;
+ wchar_t tmp[1];
+ mbstate_t state;
+ size_t nbytes;
+
+ memset (&state, '\0', sizeof (state));
+ while ((nbytes = mbrtowc (tmp, s, len, &state)) > 0)
+ @{
+ if (nbytes >= (size_t) -2)
+ /* Invalid input string. */
+ return NULL;
+ *wcp++ = towupper (tmp[0]);
+ len -= nbytes;
+ s += nbytes;
+ @}
+ return result;
+@}
+@end smallexample
+
+The use of @code{mbrtowc} should be clear. A single wide character is
+stored in @code{@var{tmp}[0]}, and the number of consumed bytes is stored
+in the variable @var{nbytes}. If the conversion is successful, the
+uppercase variant of the wide character is stored in the @var{result}
+array and the pointer to the input string and the number of available
+bytes is adjusted.
+
+The only non-obvious thing about @code{mbrtowc} might be the way memory
+is allocated for the result. The above code uses the fact that there
+can never be more wide characters in the converted results than there are
+bytes in the multibyte input string. This method yields a pessimistic
+guess about the size of the result, and if many wide character strings
+have to be constructed this way or if the strings are long, the extra
+memory required to be allocated because the input string contains
+multibyte characters might be significant. The allocated memory block can
+be resized to the correct size before returning it, but a better solution
+might be to allocate just the right amount of space for the result right
+away. Unfortunately there is no function to compute the length of the wide
+character string directly from the multibyte string. There is, however, a
+function that does part of the work.
+
+@comment wchar.h
+@comment ISO
+@deftypefun size_t mbrlen (const char *restrict @var{s}, size_t @var{n}, mbstate_t *@var{ps})
+The @code{mbrlen} function (``multibyte restartable length'') computes
+the number of at most @var{n} bytes starting at @var{s}, which form the
+next valid and complete multibyte character.
+
+If the next multibyte character corresponds to the NUL wide character,
+the return value is @math{0}. If the next @var{n} bytes form a valid
+multibyte character, the number of bytes belonging to this multibyte
+character byte sequence is returned.
+
+If the first @var{n} bytes possibly form a valid multibyte
+character but the character is incomplete, the return value is
+@code{(size_t) -2}. Otherwise the multibyte character sequence is invalid
+and the return value is @code{(size_t) -1}.
+
+The multibyte sequence is interpreted in the state represented by the
+object pointed to by @var{ps}. If @var{ps} is a null pointer, a state
+object local to @code{mbrlen} is used.
+
+@pindex wchar.h
+@code{mbrlen} was introduced in @w{Amendment 1} to @w{ISO C90} and
+is declared in @file{wchar.h}.
+@end deftypefun
+
+The attentive reader now will note that @code{mbrlen} can be implemented
+as
+
+@smallexample
+mbrtowc (NULL, s, n, ps != NULL ? ps : &internal)
+@end smallexample
+
+This is true and in fact is mentioned in the official specification.
+How can this function be used to determine the length of the wide
+character string created from a multibyte character string? It is not
+directly usable, but we can define a function @code{mbslen} using it:
+
+@smallexample
+size_t
+mbslen (const char *s)
+@{
+ mbstate_t state;
+ size_t result = 0;
+ size_t nbytes;
+ memset (&state, '\0', sizeof (state));
+ while ((nbytes = mbrlen (s, MB_LEN_MAX, &state)) > 0)
+ @{
+ if (nbytes >= (size_t) -2)
+ /* @r{Something is wrong.} */
+ return (size_t) -1;
+ s += nbytes;
+ ++result;
+ @}
+ return result;
+@}
+@end smallexample
+
+This function simply calls @code{mbrlen} for each multibyte character
+in the string and counts the number of function calls. Please note that
+we here use @code{MB_LEN_MAX} as the size argument in the @code{mbrlen}
+call. This is acceptable since a) this value is larger then the length of
+the longest multibyte character sequence and b) we know that the string
+@var{s} ends with a NUL byte, which cannot be part of any other multibyte
+character sequence but the one representing the NUL wide character.
+Therefore, the @code{mbrlen} function will never read invalid memory.
+
+Now that this function is available (just to make this clear, this
+function is @emph{not} part of the GNU C library) we can compute the
+number of wide character required to store the converted multibyte
+character string @var{s} using
+
+@smallexample
+wcs_bytes = (mbslen (s) + 1) * sizeof (wchar_t);
+@end smallexample
+
+Please note that the @code{mbslen} function is quite inefficient. The
+implementation of @code{mbstouwcs} with @code{mbslen} would have to
+perform the conversion of the multibyte character input string twice, and
+this conversion might be quite expensive. So it is necessary to think
+about the consequences of using the easier but imprecise method before
+doing the work twice.
+
+@comment wchar.h
+@comment ISO
+@deftypefun size_t wcrtomb (char *restrict @var{s}, wchar_t @var{wc}, mbstate_t *restrict @var{ps})
+The @code{wcrtomb} function (``wide character restartable to
+multibyte'') converts a single wide character into a multibyte string
+corresponding to that wide character.
+
+If @var{s} is a null pointer, the function resets the state stored in
+the objects pointed to by @var{ps} (or the internal @code{mbstate_t}
+object) to the initial state. This can also be achieved by a call like
+this:
+
+@smallexample
+wcrtombs (temp_buf, L'\0', ps)
+@end smallexample
+
+@noindent
+since, if @var{s} is a null pointer, @code{wcrtomb} performs as if it
+writes into an internal buffer, which is guaranteed to be large enough.
+
+If @var{wc} is the NUL wide character, @code{wcrtomb} emits, if
+necessary, a shift sequence to get the state @var{ps} into the initial
+state followed by a single NUL byte, which is stored in the string
+@var{s}.
+
+Otherwise a byte sequence (possibly including shift sequences) is written
+into the string @var{s}. This only happens if @var{wc} is a valid wide
+character (i.e., it has a multibyte representation in the character set
+selected by locale of the @code{LC_CTYPE} category). If @var{wc} is no
+valid wide character, nothing is stored in the strings @var{s},
+@code{errno} is set to @code{EILSEQ}, the conversion state in @var{ps}
+is undefined and the return value is @code{(size_t) -1}.
+
+If no error occurred the function returns the number of bytes stored in
+the string @var{s}. This includes all bytes representing shift
+sequences.
+
+One word about the interface of the function: there is no parameter
+specifying the length of the array @var{s}. Instead the function
+assumes that there are at least @code{MB_CUR_MAX} bytes available since
+this is the maximum length of any byte sequence representing a single
+character. So the caller has to make sure that there is enough space
+available, otherwise buffer overruns can occur.
+
+@pindex wchar.h
+@code{wcrtomb} was introduced in @w{Amendment 1} to @w{ISO C90} and is
+declared in @file{wchar.h}.
+@end deftypefun
+
+Using @code{wcrtomb} is as easy as using @code{mbrtowc}. The following
+example appends a wide character string to a multibyte character string.
+Again, the code is not really useful (or correct), it is simply here to
+demonstrate the use and some problems.
+
+@smallexample
+char *
+mbscatwcs (char *s, size_t len, const wchar_t *ws)
+@{
+ mbstate_t state;
+ /* @r{Find the end of the existing string.} */
+ char *wp = strchr (s, '\0');
+ len -= wp - s;
+ memset (&state, '\0', sizeof (state));
+ do
+ @{
+ size_t nbytes;
+ if (len < MB_CUR_LEN)
+ @{
+ /* @r{We cannot guarantee that the next}
+ @r{character fits into the buffer, so}
+ @r{return an error.} */
+ errno = E2BIG;
+ return NULL;
+ @}
+ nbytes = wcrtomb (wp, *ws, &state);
+ if (nbytes == (size_t) -1)
+ /* @r{Error in the conversion.} */
+ return NULL;
+ len -= nbytes;
+ wp += nbytes;
+ @}
+ while (*ws++ != L'\0');
+ return s;
+@}
+@end smallexample
+
+First the function has to find the end of the string currently in the
+array @var{s}. The @code{strchr} call does this very efficiently since a
+requirement for multibyte character representations is that the NUL byte
+is never used except to represent itself (and in this context, the end
+of the string).
+
+After initializing the state object the loop is entered where the first
+task is to make sure there is enough room in the array @var{s}. We
+abort if there are not at least @code{MB_CUR_LEN} bytes available. This
+is not always optimal but we have no other choice. We might have less
+than @code{MB_CUR_LEN} bytes available but the next multibyte character
+might also be only one byte long. At the time the @code{wcrtomb} call
+returns it is too late to decide whether the buffer was large enough. If
+this solution is unsuitable, there is a very slow but more accurate
+solution.
+
+@smallexample
+ @dots{}
+ if (len < MB_CUR_LEN)
+ @{
+ mbstate_t temp_state;
+ memcpy (&temp_state, &state, sizeof (state));
+ if (wcrtomb (NULL, *ws, &temp_state) > len)
+ @{
+ /* @r{We cannot guarantee that the next}
+ @r{character fits into the buffer, so}
+ @r{return an error.} */
+ errno = E2BIG;
+ return NULL;
+ @}
+ @}
+ @dots{}
+@end smallexample
+
+Here we perform the conversion that might overflow the buffer so that
+we are afterwards in the position to make an exact decision about the
+buffer size. Please note the @code{NULL} argument for the destination
+buffer in the new @code{wcrtomb} call; since we are not interested in the
+converted text at this point, this is a nice way to express this. The
+most unusual thing about this piece of code certainly is the duplication
+of the conversion state object, but if a change of the state is necessary
+to emit the next multibyte character, we want to have the same shift state
+change performed in the real conversion. Therefore, we have to preserve
+the initial shift state information.
+
+There are certainly many more and even better solutions to this problem.
+This example is only provided for educational purposes.
+
+@node Converting Strings
+@subsection Converting Multibyte and Wide Character Strings
+
+The functions described in the previous section only convert a single
+character at a time. Most operations to be performed in real-world
+programs include strings and therefore the @w{ISO C} standard also
+defines conversions on entire strings. However, the defined set of
+functions is quite limited; therefore, the GNU C library contains a few
+extensions that can help in some important situations.
+
+@comment wchar.h
+@comment ISO
+@deftypefun size_t mbsrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
+The @code{mbsrtowcs} function (``multibyte string restartable to wide
+character string'') converts an NUL-terminated multibyte character
+string at @code{*@var{src}} into an equivalent wide character string,
+including the NUL wide character at the end. The conversion is started
+using the state information from the object pointed to by @var{ps} or
+from an internal object of @code{mbsrtowcs} if @var{ps} is a null
+pointer. Before returning, the state object is updated to match the state
+after the last converted character. The state is the initial state if the
+terminating NUL byte is reached and converted.
+
+If @var{dst} is not a null pointer, the result is stored in the array
+pointed to by @var{dst}; otherwise, the conversion result is not
+available since it is stored in an internal buffer.
+
+If @var{len} wide characters are stored in the array @var{dst} before
+reaching the end of the input string, the conversion stops and @var{len}
+is returned. If @var{dst} is a null pointer, @var{len} is never checked.
+
+Another reason for a premature return from the function call is if the
+input string contains an invalid multibyte sequence. In this case the
+global variable @code{errno} is set to @code{EILSEQ} and the function
+returns @code{(size_t) -1}.
+
+@c XXX The ISO C9x draft seems to have a problem here. It says that PS
+@c is not updated if DST is NULL. This is not said straightforward and
+@c none of the other functions is described like this. It would make sense
+@c to define the function this way but I don't think it is meant like this.
+
+In all other cases the function returns the number of wide characters
+converted during this call. If @var{dst} is not null, @code{mbsrtowcs}
+stores in the pointer pointed to by @var{src} either a null pointer (if
+the NUL byte in the input string was reached) or the address of the byte
+following the last converted multibyte character.
+
+@pindex wchar.h
+@code{mbsrtowcs} was introduced in @w{Amendment 1} to @w{ISO C90} and is
+declared in @file{wchar.h}.
+@end deftypefun
+
+The definition of the @code{mbsrtowcs} function has one important
+limitation. The requirement that @var{dst} has to be a NUL-terminated
+string provides problems if one wants to convert buffers with text. A
+buffer is normally no collection of NUL-terminated strings but instead a
+continuous collection of lines, separated by newline characters. Now
+assume that a function to convert one line from a buffer is needed. Since
+the line is not NUL-terminated, the source pointer cannot directly point
+into the unmodified text buffer. This means, either one inserts the NUL
+byte at the appropriate place for the time of the @code{mbsrtowcs}
+function call (which is not doable for a read-only buffer or in a
+multi-threaded application) or one copies the line in an extra buffer
+where it can be terminated by a NUL byte. Note that it is not in general
+possible to limit the number of characters to convert by setting the
+parameter @var{len} to any specific value. Since it is not known how
+many bytes each multibyte character sequence is in length, one can only
+guess.
+
+@cindex stateful
+There is still a problem with the method of NUL-terminating a line right
+after the newline character, which could lead to very strange results.
+As said in the description of the @code{mbsrtowcs} function above the
+conversion state is guaranteed to be in the initial shift state after
+processing the NUL byte at the end of the input string. But this NUL
+byte is not really part of the text (i.e., the conversion state after
+the newline in the original text could be something different than the
+initial shift state and therefore the first character of the next line
+is encoded using this state). But the state in question is never
+accessible to the user since the conversion stops after the NUL byte
+(which resets the state). Most stateful character sets in use today
+require that the shift state after a newline be the initial state--but
+this is not a strict guarantee. Therefore, simply NUL-terminating a
+piece of a running text is not always an adequate solution and,
+therefore, should never be used in generally used code.
+
+The generic conversion interface (@pxref{Generic Charset Conversion})
+does not have this limitation (it simply works on buffers, not
+strings), and the GNU C library contains a set of functions that take
+additional parameters specifying the maximal number of bytes that are
+consumed from the input string. This way the problem of
+@code{mbsrtowcs}'s example above could be solved by determining the line
+length and passing this length to the function.
+
+@comment wchar.h
+@comment ISO
+@deftypefun size_t wcsrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps})
+The @code{wcsrtombs} function (``wide character string restartable to
+multibyte string'') converts the NUL-terminated wide character string at
+@code{*@var{src}} into an equivalent multibyte character string and
+stores the result in the array pointed to by @var{dst}. The NUL wide
+character is also converted. The conversion starts in the state
+described in the object pointed to by @var{ps} or by a state object
+locally to @code{wcsrtombs} in case @var{ps} is a null pointer. If
+@var{dst} is a null pointer, the conversion is performed as usual but the
+result is not available. If all characters of the input string were
+successfully converted and if @var{dst} is not a null pointer, the
+pointer pointed to by @var{src} gets assigned a null pointer.
+
+If one of the wide characters in the input string has no valid multibyte
+character equivalent, the conversion stops early, sets the global
+variable @code{errno} to @code{EILSEQ}, and returns @code{(size_t) -1}.
+
+Another reason for a premature stop is if @var{dst} is not a null
+pointer and the next converted character would require more than
+@var{len} bytes in total to the array @var{dst}. In this case (and if
+@var{dest} is not a null pointer) the pointer pointed to by @var{src} is
+assigned a value pointing to the wide character right after the last one
+successfully converted.
+
+Except in the case of an encoding error the return value of the
+@code{wcsrtombs} function is the number of bytes in all the multibyte
+character sequences stored in @var{dst}. Before returning the state in
+the object pointed to by @var{ps} (or the internal object in case
+@var{ps} is a null pointer) is updated to reflect the state after the
+last conversion. The state is the initial shift state in case the
+terminating NUL wide character was converted.
+
+@pindex wchar.h
+The @code{wcsrtombs} function was introduced in @w{Amendment 1} to
+@w{ISO C90} and is declared in @file{wchar.h}.
+@end deftypefun
+
+The restriction mentioned above for the @code{mbsrtowcs} function applies
+here also. There is no possibility of directly controlling the number of
+input characters. One has to place the NUL wide character at the correct
+place or control the consumed input indirectly via the available output
+array size (the @var{len} parameter).
+
+@comment wchar.h
+@comment GNU
+@deftypefun size_t mbsnrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{nmc}, size_t @var{len}, mbstate_t *restrict @var{ps})
+The @code{mbsnrtowcs} function is very similar to the @code{mbsrtowcs}
+function. All the parameters are the same except for @var{nmc}, which is
+new. The return value is the same as for @code{mbsrtowcs}.
+
+This new parameter specifies how many bytes at most can be used from the
+multibyte character string. In other words, the multibyte character
+string @code{*@var{src}} need not be NUL-terminated. But if a NUL byte
+is found within the @var{nmc} first bytes of the string, the conversion
+stops here.
+
+This function is a GNU extension. It is meant to work around the
+problems mentioned above. Now it is possible to convert a buffer with
+multibyte character text piece for piece without having to care about
+inserting NUL bytes and the effect of NUL bytes on the conversion state.
+@end deftypefun
+
+A function to convert a multibyte string into a wide character string
+and display it could be written like this (this is not a really useful
+example):
+
+@smallexample
+void
+showmbs (const char *src, FILE *fp)
+@{
+ mbstate_t state;
+ int cnt = 0;
+ memset (&state, '\0', sizeof (state));
+ while (1)
+ @{
+ wchar_t linebuf[100];
+ const char *endp = strchr (src, '\n');
+ size_t n;
+
+ /* @r{Exit if there is no more line.} */
+ if (endp == NULL)
+ break;
+
+ n = mbsnrtowcs (linebuf, &src, endp - src, 99, &state);
+ linebuf[n] = L'\0';
+ fprintf (fp, "line %d: \"%S\"\n", linebuf);
+ @}
+@}
+@end smallexample
+
+There is no problem with the state after a call to @code{mbsnrtowcs}.
+Since we don't insert characters in the strings that were not in there
+right from the beginning and we use @var{state} only for the conversion
+of the given buffer, there is no problem with altering the state.
+
+@comment wchar.h
+@comment GNU
+@deftypefun size_t wcsnrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{nwc}, size_t @var{len}, mbstate_t *restrict @var{ps})
+The @code{wcsnrtombs} function implements the conversion from wide
+character strings to multibyte character strings. It is similar to
+@code{wcsrtombs} but, just like @code{mbsnrtowcs}, it takes an extra
+parameter, which specifies the length of the input string.
+
+No more than @var{nwc} wide characters from the input string
+@code{*@var{src}} are converted. If the input string contains a NUL
+wide character in the first @var{nwc} characters, the conversion stops at
+this place.
+
+The @code{wcsnrtombs} function is a GNU extension and just like
+@code{mbsnrtowcs} helps in situations where no NUL-terminated input
+strings are available.
+@end deftypefun
+
+
+@node Multibyte Conversion Example
+@subsection A Complete Multibyte Conversion Example
+
+The example programs given in the last sections are only brief and do
+not contain all the error checking, etc. Presented here is a complete
+and documented example. It features the @code{mbrtowc} function but it
+should be easy to derive versions using the other functions.
+
+@smallexample
+int
+file_mbsrtowcs (int input, int output)
+@{
+ /* @r{Note the use of @code{MB_LEN_MAX}.}
+ @r{@code{MB_CUR_MAX} cannot portably be used here.} */
+ char buffer[BUFSIZ + MB_LEN_MAX];
+ mbstate_t state;
+ int filled = 0;
+ int eof = 0;
+
+ /* @r{Initialize the state.} */
+ memset (&state, '\0', sizeof (state));
+
+ while (!eof)
+ @{
+ ssize_t nread;
+ ssize_t nwrite;
+ char *inp = buffer;
+ wchar_t outbuf[BUFSIZ];
+ wchar_t *outp = outbuf;
+
+ /* @r{Fill up the buffer from the input file.} */
+ nread = read (input, buffer + filled, BUFSIZ);
+ if (nread < 0)
+ @{
+ perror ("read");
+ return 0;
+ @}
+ /* @r{If we reach end of file, make a note to read no more.} */
+ if (nread == 0)
+ eof = 1;
+
+ /* @r{@code{filled} is now the number of bytes in @code{buffer}.} */
+ filled += nread;
+
+ /* @r{Convert those bytes to wide characters--as many as we can.} */
+ while (1)
+ @{
+ size_t thislen = mbrtowc (outp, inp, filled, &state);
+ /* @r{Stop converting at invalid character;}
+ @r{this can mean we have read just the first part}
+ @r{of a valid character.} */
+ if (thislen == (size_t) -1)
+ break;
+ /* @r{We want to handle embedded NUL bytes}
+ @r{but the return value is 0. Correct this.} */
+ if (thislen == 0)
+ thislen = 1;
+ /* @r{Advance past this character.} */
+ inp += thislen;
+ filled -= thislen;
+ ++outp;
+ @}
+
+ /* @r{Write the wide characters we just made.} */
+ nwrite = write (output, outbuf,
+ (outp - outbuf) * sizeof (wchar_t));
+ if (nwrite < 0)
+ @{
+ perror ("write");
+ return 0;
+ @}
+
+ /* @r{See if we have a @emph{real} invalid character.} */
+ if ((eof && filled > 0) || filled >= MB_CUR_MAX)
+ @{
+ error (0, 0, "invalid multibyte character");
+ return 0;
+ @}
+
+ /* @r{If any characters must be carried forward,}
+ @r{put them at the beginning of @code{buffer}.} */
+ if (filled > 0)
+ memmove (buffer, inp, filled);
+ @}
+
+ return 1;
+@}
+@end smallexample
+
+
+@node Non-reentrant Conversion
+@section Non-reentrant Conversion Function
+
+The functions described in the previous chapter are defined in
+@w{Amendment 1} to @w{ISO C90}, but the original @w{ISO C90} standard
+also contained functions for character set conversion. The reason that
+these original functions are not described first is that they are almost
+entirely useless.
+
+The problem is that all the conversion functions described in the
+original @w{ISO C90} use a local state. Using a local state implies that
+multiple conversions at the same time (not only when using threads)
+cannot be done, and that you cannot first convert single characters and
+then strings since you cannot tell the conversion functions which state
+to use.
+
+These original functions are therefore usable only in a very limited set
+of situations. One must complete converting the entire string before
+starting a new one, and each string/text must be converted with the same
+function (there is no problem with the library itself; it is guaranteed
+that no library function changes the state of any of these functions).
+@strong{For the above reasons it is highly requested that the functions
+described in the previous section be used in place of non-reentrant
+conversion functions.}
+
+@menu
+* Non-reentrant Character Conversion:: Non-reentrant Conversion of Single
+ Characters.
+* Non-reentrant String Conversion:: Non-reentrant Conversion of Strings.
+* Shift State:: States in Non-reentrant Functions.
+@end menu
+
+@node Non-reentrant Character Conversion
+@subsection Non-reentrant Conversion of Single Characters
+
+@comment stdlib.h
+@comment ISO
+@deftypefun int mbtowc (wchar_t *restrict @var{result}, const char *restrict @var{string}, size_t @var{size})
+The @code{mbtowc} (``multibyte to wide character'') function when called
+with non-null @var{string} converts the first multibyte character
+beginning at @var{string} to its corresponding wide character code. It
+stores the result in @code{*@var{result}}.
+
+@code{mbtowc} never examines more than @var{size} bytes. (The idea is
+to supply for @var{size} the number of bytes of data you have in hand.)
+
+@code{mbtowc} with non-null @var{string} distinguishes three
+possibilities: the first @var{size} bytes at @var{string} start with
+valid multibyte characters, they start with an invalid byte sequence or
+just part of a character, or @var{string} points to an empty string (a
+null character).
+
+For a valid multibyte character, @code{mbtowc} converts it to a wide
+character and stores that in @code{*@var{result}}, and returns the
+number of bytes in that character (always at least @math{1} and never
+more than @var{size}).
+
+For an invalid byte sequence, @code{mbtowc} returns @math{-1}. For an
+empty string, it returns @math{0}, also storing @code{'\0'} in
+@code{*@var{result}}.
+
+If the multibyte character code uses shift characters, then
+@code{mbtowc} maintains and updates a shift state as it scans. If you
+call @code{mbtowc} with a null pointer for @var{string}, that
+initializes the shift state to its standard initial value. It also
+returns nonzero if the multibyte character code in use actually has a
+shift state. @xref{Shift State}.
+@end deftypefun
+
+@comment stdlib.h
+@comment ISO
+@deftypefun int wctomb (char *@var{string}, wchar_t @var{wchar})
+The @code{wctomb} (``wide character to multibyte'') function converts
+the wide character code @var{wchar} to its corresponding multibyte
+character sequence, and stores the result in bytes starting at
+@var{string}. At most @code{MB_CUR_MAX} characters are stored.
+
+@code{wctomb} with non-null @var{string} distinguishes three
+possibilities for @var{wchar}: a valid wide character code (one that can
+be translated to a multibyte character), an invalid code, and
+@code{L'\0'}.
+
+Given a valid code, @code{wctomb} converts it to a multibyte character,
+storing the bytes starting at @var{string}. Then it returns the number
+of bytes in that character (always at least @math{1} and never more
+than @code{MB_CUR_MAX}).
+
+If @var{wchar} is an invalid wide character code, @code{wctomb} returns
+@math{-1}. If @var{wchar} is @code{L'\0'}, it returns @code{0}, also
+storing @code{'\0'} in @code{*@var{string}}.
+
+If the multibyte character code uses shift characters, then
+@code{wctomb} maintains and updates a shift state as it scans. If you
+call @code{wctomb} with a null pointer for @var{string}, that
+initializes the shift state to its standard initial value. It also
+returns nonzero if the multibyte character code in use actually has a
+shift state. @xref{Shift State}.
+
+Calling this function with a @var{wchar} argument of zero when
+@var{string} is not null has the side-effect of reinitializing the
+stored shift state @emph{as well as} storing the multibyte character
+@code{'\0'} and returning @math{0}.
+@end deftypefun
+
+Similar to @code{mbrlen} there is also a non-reentrant function that
+computes the length of a multibyte character. It can be defined in
+terms of @code{mbtowc}.
+
+@comment stdlib.h
+@comment ISO
+@deftypefun int mblen (const char *@var{string}, size_t @var{size})
+The @code{mblen} function with a non-null @var{string} argument returns
+the number of bytes that make up the multibyte character beginning at
+@var{string}, never examining more than @var{size} bytes. (The idea is
+to supply for @var{size} the number of bytes of data you have in hand.)
+
+The return value of @code{mblen} distinguishes three possibilities: the
+first @var{size} bytes at @var{string} start with valid multibyte
+characters, they start with an invalid byte sequence or just part of a
+character, or @var{string} points to an empty string (a null character).
+
+For a valid multibyte character, @code{mblen} returns the number of
+bytes in that character (always at least @code{1} and never more than
+@var{size}). For an invalid byte sequence, @code{mblen} returns
+@math{-1}. For an empty string, it returns @math{0}.
+
+If the multibyte character code uses shift characters, then @code{mblen}
+maintains and updates a shift state as it scans. If you call
+@code{mblen} with a null pointer for @var{string}, that initializes the
+shift state to its standard initial value. It also returns a nonzero
+value if the multibyte character code in use actually has a shift state.
+@xref{Shift State}.
+
+@pindex stdlib.h
+The function @code{mblen} is declared in @file{stdlib.h}.
+@end deftypefun
+
+
+@node Non-reentrant String Conversion
+@subsection Non-reentrant Conversion of Strings
+
+For convenience the @w{ISO C90} standard also defines functions to
+convert entire strings instead of single characters. These functions
+suffer from the same problems as their reentrant counterparts from
+@w{Amendment 1} to @w{ISO C90}; see @ref{Converting Strings}.
+
+@comment stdlib.h
+@comment ISO
+@deftypefun size_t mbstowcs (wchar_t *@var{wstring}, const char *@var{string}, size_t @var{size})
+The @code{mbstowcs} (``multibyte string to wide character string'')
+function converts the null-terminated string of multibyte characters
+@var{string} to an array of wide character codes, storing not more than
+@var{size} wide characters into the array beginning at @var{wstring}.
+The terminating null character counts towards the size, so if @var{size}
+is less than the actual number of wide characters resulting from
+@var{string}, no terminating null character is stored.
+
+The conversion of characters from @var{string} begins in the initial
+shift state.
+
+If an invalid multibyte character sequence is found, the @code{mbstowcs}
+function returns a value of @math{-1}. Otherwise, it returns the number
+of wide characters stored in the array @var{wstring}. This number does
+not include the terminating null character, which is present if the
+number is less than @var{size}.
+
+Here is an example showing how to convert a string of multibyte
+characters, allocating enough space for the result.
+
+@smallexample
+wchar_t *
+mbstowcs_alloc (const char *string)
+@{
+ size_t size = strlen (string) + 1;
+ wchar_t *buf = xmalloc (size * sizeof (wchar_t));
+
+ size = mbstowcs (buf, string, size);
+ if (size == (size_t) -1)
+ return NULL;
+ buf = xrealloc (buf, (size + 1) * sizeof (wchar_t));
+ return buf;
+@}
+@end smallexample
+
+@end deftypefun
+
+@comment stdlib.h
+@comment ISO
+@deftypefun size_t wcstombs (char *@var{string}, const wchar_t *@var{wstring}, size_t @var{size})
+The @code{wcstombs} (``wide character string to multibyte string'')
+function converts the null-terminated wide character array @var{wstring}
+into a string containing multibyte characters, storing not more than
+@var{size} bytes starting at @var{string}, followed by a terminating
+null character if there is room. The conversion of characters begins in
+the initial shift state.
+
+The terminating null character counts towards the size, so if @var{size}
+is less than or equal to the number of bytes needed in @var{wstring}, no
+terminating null character is stored.
+
+If a code that does not correspond to a valid multibyte character is
+found, the @code{wcstombs} function returns a value of @math{-1}.
+Otherwise, the return value is the number of bytes stored in the array
+@var{string}. This number does not include the terminating null character,
+which is present if the number is less than @var{size}.
+@end deftypefun
+
+@node Shift State
+@subsection States in Non-reentrant Functions
+
+In some multibyte character codes, the @emph{meaning} of any particular
+byte sequence is not fixed; it depends on what other sequences have come
+earlier in the same string. Typically there are just a few sequences that
+can change the meaning of other sequences; these few are called
+@dfn{shift sequences} and we say that they set the @dfn{shift state} for
+other sequences that follow.
+
+To illustrate shift state and shift sequences, suppose we decide that
+the sequence @code{0200} (just one byte) enters Japanese mode, in which
+pairs of bytes in the range from @code{0240} to @code{0377} are single
+characters, while @code{0201} enters Latin-1 mode, in which single bytes
+in the range from @code{0240} to @code{0377} are characters, and
+interpreted according to the ISO Latin-1 character set. This is a
+multibyte code that has two alternative shift states (``Japanese mode''
+and ``Latin-1 mode''), and two shift sequences that specify particular
+shift states.
+
+When the multibyte character code in use has shift states, then
+@code{mblen}, @code{mbtowc}, and @code{wctomb} must maintain and update
+the current shift state as they scan the string. To make this work
+properly, you must follow these rules:
+
+@itemize @bullet
+@item
+Before starting to scan a string, call the function with a null pointer
+for the multibyte character address---for example, @code{mblen (NULL,
+0)}. This initializes the shift state to its standard initial value.
+
+@item
+Scan the string one character at a time, in order. Do not ``back up''
+and rescan characters already scanned, and do not intersperse the
+processing of different strings.
+@end itemize
+
+Here is an example of using @code{mblen} following these rules:
+
+@smallexample
+void
+scan_string (char *s)
+@{
+ int length = strlen (s);
+
+ /* @r{Initialize shift state.} */
+ mblen (NULL, 0);
+
+ while (1)
+ @{
+ int thischar = mblen (s, length);
+ /* @r{Deal with end of string and invalid characters.} */
+ if (thischar == 0)
+ break;
+ if (thischar == -1)
+ @{
+ error ("invalid multibyte character");
+ break;
+ @}
+ /* @r{Advance past this character.} */
+ s += thischar;
+ length -= thischar;
+ @}
+@}
+@end smallexample
+
+The functions @code{mblen}, @code{mbtowc} and @code{wctomb} are not
+reentrant when using a multibyte code that uses a shift state. However,
+no other library functions call these functions, so you don't have to
+worry that the shift state will be changed mysteriously.
+
+
+@node Generic Charset Conversion
+@section Generic Charset Conversion
+
+The conversion functions mentioned so far in this chapter all had in
+common that they operate on character sets that are not directly
+specified by the functions. The multibyte encoding used is specified by
+the currently selected locale for the @code{LC_CTYPE} category. The
+wide character set is fixed by the implementation (in the case of GNU C
+library it is always UCS-4 encoded @w{ISO 10646}.
+
+This has of course several problems when it comes to general character
+conversion:
+
+@itemize @bullet
+@item
+For every conversion where neither the source nor the destination
+character set is the character set of the locale for the @code{LC_CTYPE}
+category, one has to change the @code{LC_CTYPE} locale using
+@code{setlocale}.
+
+Changing the @code{LC_TYPE} locale introduces major problems for the rest
+of the programs since several more functions (e.g., the character
+classification functions, @pxref{Classification of Characters}) use the
+@code{LC_CTYPE} category.
+
+@item
+Parallel conversions to and from different character sets are not
+possible since the @code{LC_CTYPE} selection is global and shared by all
+threads.
+
+@item
+If neither the source nor the destination character set is the character
+set used for @code{wchar_t} representation, there is at least a two-step
+process necessary to convert a text using the functions above. One would
+have to select the source character set as the multibyte encoding,
+convert the text into a @code{wchar_t} text, select the destination
+character set as the multibyte encoding, and convert the wide character
+text to the multibyte (@math{=} destination) character set.
+
+Even if this is possible (which is not guaranteed) it is a very tiring
+work. Plus it suffers from the other two raised points even more due to
+the steady changing of the locale.
+@end itemize
+
+The XPG2 standard defines a completely new set of functions, which has
+none of these limitations. They are not at all coupled to the selected
+locales, and they have no constraints on the character sets selected for
+source and destination. Only the set of available conversions limits
+them. The standard does not specify that any conversion at all must be
+available. Such availability is a measure of the quality of the
+implementation.
+
+In the following text first the interface to @code{iconv} and then the
+conversion function, will be described. Comparisons with other
+implementations will show what obstacles stand in the way of portable
+applications. Finally, the implementation is described in so far as might
+interest the advanced user who wants to extend conversion capabilities.
+
+@menu
+* Generic Conversion Interface:: Generic Character Set Conversion Interface.
+* iconv Examples:: A complete @code{iconv} example.
+* Other iconv Implementations:: Some Details about other @code{iconv}
+ Implementations.
+* glibc iconv Implementation:: The @code{iconv} Implementation in the GNU C
+ library.
+@end menu
+
+@node Generic Conversion Interface
+@subsection Generic Character Set Conversion Interface
+
+This set of functions follows the traditional cycle of using a resource:
+open--use--close. The interface consists of three functions, each of
+which implements one step.
+
+Before the interfaces are described it is necessary to introduce a
+data type. Just like other open--use--close interfaces the functions
+introduced here work using handles and the @file{iconv.h} header
+defines a special type for the handles used.
+
+@comment iconv.h
+@comment XPG2
+@deftp {Data Type} iconv_t
+This data type is an abstract type defined in @file{iconv.h}. The user
+must not assume anything about the definition of this type; it must be
+completely opaque.
+
+Objects of this type can get assigned handles for the conversions using
+the @code{iconv} functions. The objects themselves need not be freed, but
+the conversions for which the handles stand for have to.
+@end deftp
+
+@noindent
+The first step is the function to create a handle.
+
+@comment iconv.h
+@comment XPG2
+@deftypefun iconv_t iconv_open (const char *@var{tocode}, const char *@var{fromcode})
+The @code{iconv_open} function has to be used before starting a
+conversion. The two parameters this function takes determine the
+source and destination character set for the conversion, and if the
+implementation has the possibility to perform such a conversion, the
+function returns a handle.
+
+If the wanted conversion is not available, the @code{iconv_open} function
+returns @code{(iconv_t) -1}. In this case the global variable
+@code{errno} can have the following values:
+
+@table @code
+@item EMFILE
+The process already has @code{OPEN_MAX} file descriptors open.
+@item ENFILE
+The system limit of open file is reached.
+@item ENOMEM
+Not enough memory to carry out the operation.
+@item EINVAL
+The conversion from @var{fromcode} to @var{tocode} is not supported.
+@end table
+
+It is not possible to use the same descriptor in different threads to
+perform independent conversions. The data structures associated
+with the descriptor include information about the conversion state.
+This must not be messed up by using it in different conversions.
+
+An @code{iconv} descriptor is like a file descriptor as for every use a
+new descriptor must be created. The descriptor does not stand for all
+of the conversions from @var{fromset} to @var{toset}.
+
+The GNU C library implementation of @code{iconv_open} has one
+significant extension to other implementations. To ease the extension
+of the set of available conversions, the implementation allows storing
+the necessary files with data and code in an arbitrary number of
+directories. How this extension must be written will be explained below
+(@pxref{glibc iconv Implementation}). Here it is only important to say
+that all directories mentioned in the @code{GCONV_PATH} environment
+variable are considered only if they contain a file @file{gconv-modules}.
+These directories need not necessarily be created by the system
+administrator. In fact, this extension is introduced to help users
+writing and using their own, new conversions. Of course, this does not
+work for security reasons in SUID binaries; in this case only the system
+directory is considered and this normally is
+@file{@var{prefix}/lib/gconv}. The @code{GCONV_PATH} environment
+variable is examined exactly once at the first call of the
+@code{iconv_open} function. Later modifications of the variable have no
+effect.
+
+@pindex iconv.h
+The @code{iconv_open} function was introduced early in the X/Open
+Portability Guide, @w{version 2}. It is supported by all commercial
+Unices as it is required for the Unix branding. However, the quality and
+completeness of the implementation varies widely. The @code{iconv_open}
+function is declared in @file{iconv.h}.
+@end deftypefun
+
+The @code{iconv} implementation can associate large data structure with
+the handle returned by @code{iconv_open}. Therefore, it is crucial to
+free all the resources once all conversions are carried out and the
+conversion is not needed anymore.
+
+@comment iconv.h
+@comment XPG2
+@deftypefun int iconv_close (iconv_t @var{cd})
+The @code{iconv_close} function frees all resources associated with the
+handle @var{cd}, which must have been returned by a successful call to
+the @code{iconv_open} function.
+
+If the function call was successful the return value is @math{0}.
+Otherwise it is @math{-1} and @code{errno} is set appropriately.
+Defined error are:
+
+@table @code
+@item EBADF
+The conversion descriptor is invalid.
+@end table
+
+@pindex iconv.h
+The @code{iconv_close} function was introduced together with the rest
+of the @code{iconv} functions in XPG2 and is declared in @file{iconv.h}.
+@end deftypefun
+
+The standard defines only one actual conversion function. This has,
+therefore, the most general interface: it allows conversion from one
+buffer to another. Conversion from a file to a buffer, vice versa, or
+even file to file can be implemented on top of it.
+
+@comment iconv.h
+@comment XPG2
+@deftypefun size_t iconv (iconv_t @var{cd}, char **@var{inbuf}, size_t *@var{inbytesleft}, char **@var{outbuf}, size_t *@var{outbytesleft})
+@cindex stateful
+The @code{iconv} function converts the text in the input buffer
+according to the rules associated with the descriptor @var{cd} and
+stores the result in the output buffer. It is possible to call the
+function for the same text several times in a row since for stateful
+character sets the necessary state information is kept in the data
+structures associated with the descriptor.
+
+The input buffer is specified by @code{*@var{inbuf}} and it contains
+@code{*@var{inbytesleft}} bytes. The extra indirection is necessary for
+communicating the used input back to the caller (see below). It is
+important to note that the buffer pointer is of type @code{char} and the
+length is measured in bytes even if the input text is encoded in wide
+characters.
+
+The output buffer is specified in a similar way. @code{*@var{outbuf}}
+points to the beginning of the buffer with at least
+@code{*@var{outbytesleft}} bytes room for the result. The buffer
+pointer again is of type @code{char} and the length is measured in
+bytes. If @var{outbuf} or @code{*@var{outbuf}} is a null pointer, the
+conversion is performed but no output is available.
+
+If @var{inbuf} is a null pointer, the @code{iconv} function performs the
+necessary action to put the state of the conversion into the initial
+state. This is obviously a no-op for non-stateful encodings, but if the
+encoding has a state, such a function call might put some byte sequences
+in the output buffer, which perform the necessary state changes. The
+next call with @var{inbuf} not being a null pointer then simply goes on
+from the initial state. It is important that the programmer never makes
+any assumption as to whether the conversion has to deal with states.
+Even if the input and output character sets are not stateful, the
+implementation might still have to keep states. This is due to the
+implementation chosen for the GNU C library as it is described below.
+Therefore an @code{iconv} call to reset the state should always be
+performed if some protocol requires this for the output text.
+
+The conversion stops for one of three reasons. The first is that all
+characters from the input buffer are converted. This actually can mean
+two things: either all bytes from the input buffer are consumed or
+there are some bytes at the end of the buffer that possibly can form a
+complete character but the input is incomplete. The second reason for a
+stop is that the output buffer is full. And the third reason is that
+the input contains invalid characters.
+
+In all of these cases the buffer pointers after the last successful
+conversion, for input and output buffer, are stored in @var{inbuf} and
+@var{outbuf}, and the available room in each buffer is stored in
+@var{inbytesleft} and @var{outbytesleft}.
+
+Since the character sets selected in the @code{iconv_open} call can be
+almost arbitrary, there can be situations where the input buffer contains
+valid characters, which have no identical representation in the output
+character set. The behavior in this situation is undefined. The
+@emph{current} behavior of the GNU C library in this situation is to
+return with an error immediately. This certainly is not the most
+desirable solution; therefore, future versions will provide better ones,
+but they are not yet finished.
+
+If all input from the input buffer is successfully converted and stored
+in the output buffer, the function returns the number of non-reversible
+conversions performed. In all other cases the return value is
+@code{(size_t) -1} and @code{errno} is set appropriately. In such cases
+the value pointed to by @var{inbytesleft} is nonzero.
+
+@table @code
+@item EILSEQ
+The conversion stopped because of an invalid byte sequence in the input.
+After the call, @code{*@var{inbuf}} points at the first byte of the
+invalid byte sequence.
+
+@item E2BIG
+The conversion stopped because it ran out of space in the output buffer.
+
+@item EINVAL
+The conversion stopped because of an incomplete byte sequence at the end
+of the input buffer.
+
+@item EBADF
+The @var{cd} argument is invalid.
+@end table
+
+@pindex iconv.h
+The @code{iconv} function was introduced in the XPG2 standard and is
+declared in the @file{iconv.h} header.
+@end deftypefun
+
+The definition of the @code{iconv} function is quite good overall. It
+provides quite flexible functionality. The only problems lie in the
+boundary cases, which are incomplete byte sequences at the end of the
+input buffer and invalid input. A third problem, which is not really
+a design problem, is the way conversions are selected. The standard
+does not say anything about the legitimate names, a minimal set of
+available conversions. We will see how this negatively impacts other
+implementations, as demonstrated below.
+
+@node iconv Examples
+@subsection A complete @code{iconv} example
+
+The example below features a solution for a common problem. Given that
+one knows the internal encoding used by the system for @code{wchar_t}
+strings, one often is in the position to read text from a file and store
+it in wide character buffers. One can do this using @code{mbsrtowcs},
+but then we run into the problems discussed above.
+
+@smallexample
+int
+file2wcs (int fd, const char *charset, wchar_t *outbuf, size_t avail)
+@{
+ char inbuf[BUFSIZ];
+ size_t insize = 0;
+ char *wrptr = (char *) outbuf;
+ int result = 0;
+ iconv_t cd;
+
+ cd = iconv_open ("WCHAR_T", charset);
+ if (cd == (iconv_t) -1)
+ @{
+ /* @r{Something went wrong.} */
+ if (errno == EINVAL)
+ error (0, 0, "conversion from '%s' to wchar_t not available",
+ charset);
+ else
+ perror ("iconv_open");
+
+ /* @r{Terminate the output string.} */
+ *outbuf = L'\0';
+
+ return -1;
+ @}
+
+ while (avail > 0)
+ @{
+ size_t nread;
+ size_t nconv;
+ char *inptr = inbuf;
+
+ /* @r{Read more input.} */
+ nread = read (fd, inbuf + insize, sizeof (inbuf) - insize);
+ if (nread == 0)
+ @{
+ /* @r{When we come here the file is completely read.}
+ @r{This still could mean there are some unused}
+ @r{characters in the @code{inbuf}. Put them back.} */
+ if (lseek (fd, -insize, SEEK_CUR) == -1)
+ result = -1;
+
+ /* @r{Now write out the byte sequence to get into the}
+ @r{initial state if this is necessary.} */
+ iconv (cd, NULL, NULL, &wrptr, &avail);
+
+ break;
+ @}
+ insize += nread;
+
+ /* @r{Do the conversion.} */
+ nconv = iconv (cd, &inptr, &insize, &wrptr, &avail);
+ if (nconv == (size_t) -1)
+ @{
+ /* @r{Not everything went right. It might only be}
+ @r{an unfinished byte sequence at the end of the}
+ @r{buffer. Or it is a real problem.} */
+ if (errno == EINVAL)
+ /* @r{This is harmless. Simply move the unused}
+ @r{bytes to the beginning of the buffer so that}
+ @r{they can be used in the next round.} */
+ memmove (inbuf, inptr, insize);
+ else
+ @{
+ /* @r{It is a real problem. Maybe we ran out of}
+ @r{space in the output buffer or we have invalid}
+ @r{input. In any case back the file pointer to}
+ @r{the position of the last processed byte.} */
+ lseek (fd, -insize, SEEK_CUR);
+ result = -1;
+ break;
+ @}
+ @}
+ @}
+
+ /* @r{Terminate the output string.} */
+ if (avail >= sizeof (wchar_t))
+ *((wchar_t *) wrptr) = L'\0';
+
+ if (iconv_close (cd) != 0)
+ perror ("iconv_close");
+
+ return (wchar_t *) wrptr - outbuf;
+@}
+@end smallexample
+
+@cindex stateful
+This example shows the most important aspects of using the @code{iconv}
+functions. It shows how successive calls to @code{iconv} can be used to
+convert large amounts of text. The user does not have to care about
+stateful encodings as the functions take care of everything.
+
+An interesting point is the case where @code{iconv} returns an error and
+@code{errno} is set to @code{EINVAL}. This is not really an error in the
+transformation. It can happen whenever the input character set contains
+byte sequences of more than one byte for some character and texts are not
+processed in one piece. In this case there is a chance that a multibyte
+sequence is cut. The caller can then simply read the remainder of the
+takes and feed the offending bytes together with new character from the
+input to @code{iconv} and continue the work. The internal state kept in
+the descriptor is @emph{not} unspecified after such an event as is the
+case with the conversion functions from the @w{ISO C} standard.
+
+The example also shows the problem of using wide character strings with
+@code{iconv}. As explained in the description of the @code{iconv}
+function above, the function always takes a pointer to a @code{char}
+array and the available space is measured in bytes. In the example, the
+output buffer is a wide character buffer; therefore, we use a local
+variable @var{wrptr} of type @code{char *}, which is used in the
+@code{iconv} calls.
+
+This looks rather innocent but can lead to problems on platforms that
+have tight restriction on alignment. Therefore the caller of @code{iconv}
+has to make sure that the pointers passed are suitable for access of
+characters from the appropriate character set. Since, in the
+above case, the input parameter to the function is a @code{wchar_t}
+pointer, this is the case (unless the user violates alignment when
+computing the parameter). But in other situations, especially when
+writing generic functions where one does not know what type of character
+set one uses and, therefore, treats text as a sequence of bytes, it might
+become tricky.
+
+@node Other iconv Implementations
+@subsection Some Details about other @code{iconv} Implementations
+
+This is not really the place to discuss the @code{iconv} implementation
+of other systems but it is necessary to know a bit about them to write
+portable programs. The above mentioned problems with the specification
+of the @code{iconv} functions can lead to portability issues.
+
+The first thing to notice is that, due to the large number of character
+sets in use, it is certainly not practical to encode the conversions
+directly in the C library. Therefore, the conversion information must
+come from files outside the C library. This is usually done in one or
+both of the following ways:
+
+@itemize @bullet
+@item
+The C library contains a set of generic conversion functions that can
+read the needed conversion tables and other information from data files.
+These files get loaded when necessary.
+
+This solution is problematic as it requires a great deal of effort to
+apply to all character sets (potentially an infinite set). The
+differences in the structure of the different character sets is so large
+that many different variants of the table-processing functions must be
+developed. In addition, the generic nature of these functions make them
+slower than specifically implemented functions.
+
+@item
+The C library only contains a framework that can dynamically load
+object files and execute the conversion functions contained therein.
+
+This solution provides much more flexibility. The C library itself
+contains only very little code and therefore reduces the general memory
+footprint. Also, with a documented interface between the C library and
+the loadable modules it is possible for third parties to extend the set
+of available conversion modules. A drawback of this solution is that
+dynamic loading must be available.
+@end itemize
+
+Some implementations in commercial Unices implement a mixture of these
+possibilities; the majority implement only the second solution. Using
+loadable modules moves the code out of the library itself and keeps
+the door open for extensions and improvements, but this design is also
+limiting on some platforms since not many platforms support dynamic
+loading in statically linked programs. On platforms without this
+capability it is therefore not possible to use this interface in
+statically linked programs. The GNU C library has, on ELF platforms, no
+problems with dynamic loading in these situations; therefore, this
+point is moot. The danger is that one gets acquainted with this
+situation and forgets about the restrictions on other systems.
+
+A second thing to know about other @code{iconv} implementations is that
+the number of available conversions is often very limited. Some
+implementations provide, in the standard release (not special
+international or developer releases), at most 100 to 200 conversion
+possibilities. This does not mean 200 different character sets are
+supported; for example, conversions from one character set to a set of 10
+others might count as 10 conversions. Together with the other direction
+this makes 20 conversion possibilities used up by one character set. One
+can imagine the thin coverage these platform provide. Some Unix vendors
+even provide only a handful of conversions, which renders them useless for
+almost all uses.
+
+This directly leads to a third and probably the most problematic point.
+The way the @code{iconv} conversion functions are implemented on all
+known Unix systems and the availability of the conversion functions from
+character set @math{@cal{A}} to @math{@cal{B}} and the conversion from
+@math{@cal{B}} to @math{@cal{C}} does @emph{not} imply that the
+conversion from @math{@cal{A}} to @math{@cal{C}} is available.
+
+This might not seem unreasonable and problematic at first, but it is a
+quite big problem as one will notice shortly after hitting it. To show
+the problem we assume to write a program that has to convert from
+@math{@cal{A}} to @math{@cal{C}}. A call like
+
+@smallexample
+cd = iconv_open ("@math{@cal{C}}", "@math{@cal{A}}");
+@end smallexample
+
+@noindent
+fails according to the assumption above. But what does the program
+do now? The conversion is necessary; therefore, simply giving up is not
+an option.
+
+This is a nuisance. The @code{iconv} function should take care of this.
+But how should the program proceed from here on? If it tries to convert
+to character set @math{@cal{B}}, first the two @code{iconv_open}
+calls
+
+@smallexample
+cd1 = iconv_open ("@math{@cal{B}}", "@math{@cal{A}}");
+@end smallexample
+
+@noindent
+and
+
+@smallexample
+cd2 = iconv_open ("@math{@cal{C}}", "@math{@cal{B}}");
+@end smallexample
+
+@noindent
+will succeed, but how to find @math{@cal{B}}?
+
+Unfortunately, the answer is: there is no general solution. On some
+systems guessing might help. On those systems most character sets can
+convert to and from UTF-8 encoded @w{ISO 10646} or Unicode text. Beside
+this only some very system-specific methods can help. Since the
+conversion functions come from loadable modules and these modules must
+be stored somewhere in the filesystem, one @emph{could} try to find them
+and determine from the available file which conversions are available
+and whether there is an indirect route from @math{@cal{A}} to
+@math{@cal{C}}.
+
+This example shows one of the design errors of @code{iconv} mentioned
+above. It should at least be possible to determine the list of available
+conversion programmatically so that if @code{iconv_open} says there is no
+such conversion, one could make sure this also is true for indirect
+routes.
+
+@node glibc iconv Implementation
+@subsection The @code{iconv} Implementation in the GNU C library
+
+After reading about the problems of @code{iconv} implementations in the
+last section it is certainly good to note that the implementation in
+the GNU C library has none of the problems mentioned above. What
+follows is a step-by-step analysis of the points raised above. The
+evaluation is based on the current state of the development (as of
+January 1999). The development of the @code{iconv} functions is not
+complete, but basic functionality has solidified.
+
+The GNU C library's @code{iconv} implementation uses shared loadable
+modules to implement the conversions. A very small number of
+conversions are built into the library itself but these are only rather
+trivial conversions.
+
+All the benefits of loadable modules are available in the GNU C library
+implementation. This is especially appealing since the interface is
+well documented (see below), and it, therefore, is easy to write new
+conversion modules. The drawback of using loadable objects is not a
+problem in the GNU C library, at least on ELF systems. Since the
+library is able to load shared objects even in statically linked
+binaries, static linking need not be forbidden in case one wants to use
+@code{iconv}.
+
+The second mentioned problem is the number of supported conversions.
+Currently, the GNU C library supports more than 150 character sets. The
+way the implementation is designed the number of supported conversions
+is greater than 22350 (@math{150} times @math{149}). If any conversion
+from or to a character set is missing, it can be added easily.
+
+Particularly impressive as it may be, this high number is due to the
+fact that the GNU C library implementation of @code{iconv} does not have
+the third problem mentioned above (i.e., whenever there is a conversion
+from a character set @math{@cal{A}} to @math{@cal{B}} and from
+@math{@cal{B}} to @math{@cal{C}} it is always possible to convert from
+@math{@cal{A}} to @math{@cal{C}} directly). If the @code{iconv_open}
+returns an error and sets @code{errno} to @code{EINVAL}, there is no
+known way, directly or indirectly, to perform the wanted conversion.
+
+@cindex triangulation
+Triangulation is achieved by providing for each character set a
+conversion from and to UCS-4 encoded @w{ISO 10646}. Using @w{ISO 10646}
+as an intermediate representation it is possible to @dfn{triangulate}
+(i.e., convert with an intermediate representation).
+
+There is no inherent requirement to provide a conversion to @w{ISO
+10646} for a new character set, and it is also possible to provide other
+conversions where neither source nor destination character set is @w{ISO
+10646}. The existing set of conversions is simply meant to cover all
+conversions that might be of interest.
+
+@cindex ISO-2022-JP
+@cindex EUC-JP
+All currently available conversions use the triangulation method above,
+making conversion run unnecessarily slow. If, for example, somebody
+often needs the conversion from ISO-2022-JP to EUC-JP, a quicker solution
+would involve direct conversion between the two character sets, skipping
+the input to @w{ISO 10646} first. The two character sets of interest
+are much more similar to each other than to @w{ISO 10646}.
+
+In such a situation one easily can write a new conversion and provide it
+as a better alternative. The GNU C library @code{iconv} implementation
+would automatically use the module implementing the conversion if it is
+specified to be more efficient.
+
+@subsubsection Format of @file{gconv-modules} files
+
+All information about the available conversions comes from a file named
+@file{gconv-modules}, which can be found in any of the directories along
+the @code{GCONV_PATH}. The @file{gconv-modules} files are line-oriented
+text files, where each of the lines has one of the following formats:
+
+@itemize @bullet
+@item
+If the first non-whitespace character is a @kbd{#} the line contains only
+comments and is ignored.
+
+@item
+Lines starting with @code{alias} define an alias name for a character
+set. Two more words are expected on the line. The first word
+defines the alias name, and the second defines the original name of the
+character set. The effect is that it is possible to use the alias name
+in the @var{fromset} or @var{toset} parameters of @code{iconv_open} and
+achieve the same result as when using the real character set name.
+
+This is quite important as a character set has often many different
+names. There is normally an official name but this need not correspond to
+the most popular name. Beside this many character sets have special
+names that are somehow constructed. For example, all character sets
+specified by the ISO have an alias of the form @code{ISO-IR-@var{nnn}}
+where @var{nnn} is the registration number. This allows programs that
+know about the registration number to construct character set names and
+use them in @code{iconv_open} calls. More on the available names and
+aliases follows below.
+
+@item
+Lines starting with @code{module} introduce an available conversion
+module. These lines must contain three or four more words.
+
+The first word specifies the source character set, the second word the
+destination character set of conversion implemented in this module, and
+the third word is the name of the loadable module. The filename is
+constructed by appending the usual shared object suffix (normally
+@file{.so}) and this file is then supposed to be found in the same
+directory the @file{gconv-modules} file is in. The last word on the line,
+which is optional, is a numeric value representing the cost of the
+conversion. If this word is missing, a cost of @math{1} is assumed. The
+numeric value itself does not matter that much; what counts are the
+relative values of the sums of costs for all possible conversion paths.
+Below is a more precise description of the use of the cost value.
+@end itemize
+
+Returning to the example above where one has written a module to directly
+convert from ISO-2022-JP to EUC-JP and back. All that has to be done is
+to put the new module, let its name be ISO2022JP-EUCJP.so, in a directory
+and add a file @file{gconv-modules} with the following content in the
+same directory:
+
+@smallexample
+module ISO-2022-JP// EUC-JP// ISO2022JP-EUCJP 1
+module EUC-JP// ISO-2022-JP// ISO2022JP-EUCJP 1
+@end smallexample
+
+To see why this is sufficient, it is necessary to understand how the
+conversion used by @code{iconv} (and described in the descriptor) is
+selected. The approach to this problem is quite simple.
+
+At the first call of the @code{iconv_open} function the program reads
+all available @file{gconv-modules} files and builds up two tables: one
+containing all the known aliases and another that contains the
+information about the conversions and which shared object implements
+them.
+
+@subsubsection Finding the conversion path in @code{iconv}
+
+The set of available conversions form a directed graph with weighted
+edges. The weights on the edges are the costs specified in the
+@file{gconv-modules} files. The @code{iconv_open} function uses an
+algorithm suitable for search for the best path in such a graph and so
+constructs a list of conversions that must be performed in succession
+to get the transformation from the source to the destination character
+set.
+
+Explaining why the above @file{gconv-modules} files allows the
+@code{iconv} implementation to resolve the specific ISO-2022-JP to
+EUC-JP conversion module instead of the conversion coming with the
+library itself is straightforward. Since the latter conversion takes two
+steps (from ISO-2022-JP to @w{ISO 10646} and then from @w{ISO 10646} to
+EUC-JP), the cost is @math{1+1 = 2}. The above @file{gconv-modules}
+file, however, specifies that the new conversion modules can perform this
+conversion with only the cost of @math{1}.
+
+A mysterious item about the @file{gconv-modules} file above (and also
+the file coming with the GNU C library) are the names of the character
+sets specified in the @code{module} lines. Why do almost all the names
+end in @code{//}? And this is not all: the names can actually be
+regular expressions. At this point in time this mystery should not be
+revealed, unless you have the relevant spell-casting materials: ashes
+from an original @w{DOS 6.2} boot disk burnt in effigy, a crucifix
+blessed by St.@: Emacs, assorted herbal roots from Central America, sand
+from Cebu, etc. Sorry! @strong{The part of the implementation where
+this is used is not yet finished. For now please simply follow the
+existing examples. It'll become clearer once it is. --drepper}
+
+A last remark about the @file{gconv-modules} is about the names not
+ending with @code{//}. A character set named @code{INTERNAL} is often
+mentioned. From the discussion above and the chosen name it should have
+become clear that this is the name for the representation used in the
+intermediate step of the triangulation. We have said that this is UCS-4
+but actually that is not quite right. The UCS-4 specification also
+includes the specification of the byte ordering used. Since a UCS-4 value
+consists of four bytes, a stored value is effected by byte ordering. The
+internal representation is @emph{not} the same as UCS-4 in case the byte
+ordering of the processor (or at least the running process) is not the
+same as the one required for UCS-4. This is done for performance reasons
+as one does not want to perform unnecessary byte-swapping operations if
+one is not interested in actually seeing the result in UCS-4. To avoid
+trouble with endianness, the internal representation consistently is named
+@code{INTERNAL} even on big-endian systems where the representations are
+identical.
+
+@subsubsection @code{iconv} module data structures
+
+So far this section has described how modules are located and considered
+to be used. What remains to be described is the interface of the modules
+so that one can write new ones. This section describes the interface as
+it is in use in January 1999. The interface will change a bit in the
+future but, with luck, only in an upwardly compatible way.
+
+The definitions necessary to write new modules are publicly available
+in the non-standard header @file{gconv.h}. The following text,
+therefore, describes the definitions from this header file. First,
+however, it is necessary to get an overview.
+
+From the perspective of the user of @code{iconv} the interface is quite
+simple: the @code{iconv_open} function returns a handle that can be used
+in calls to @code{iconv}, and finally the handle is freed with a call to
+@code{iconv_close}. The problem is that the handle has to be able to
+represent the possibly long sequences of conversion steps and also the
+state of each conversion since the handle is all that is passed to the
+@code{iconv} function. Therefore, the data structures are really the
+elements necessary to understanding the implementation.
+
+We need two different kinds of data structures. The first describes the
+conversion and the second describes the state etc. There are really two
+type definitions like this in @file{gconv.h}.
+@pindex gconv.h
+
+@comment gconv.h
+@comment GNU
+@deftp {Data type} {struct __gconv_step}
+This data structure describes one conversion a module can perform. For
+each function in a loaded module with conversion functions there is
+exactly one object of this type. This object is shared by all users of
+the conversion (i.e., this object does not contain any information
+corresponding to an actual conversion; it only describes the conversion
+itself).
+
+@table @code
+@item struct __gconv_loaded_object *__shlib_handle
+@itemx const char *__modname
+@itemx int __counter
+All these elements of the structure are used internally in the C library
+to coordinate loading and unloading the shared. One must not expect any
+of the other elements to be available or initialized.
+
+@item const char *__from_name
+@itemx const char *__to_name
+@code{__from_name} and @code{__to_name} contain the names of the source and
+destination character sets. They can be used to identify the actual
+conversion to be carried out since one module might implement conversions
+for more than one character set and/or direction.
+
+@item gconv_fct __fct
+@itemx gconv_init_fct __init_fct
+@itemx gconv_end_fct __end_fct
+These elements contain pointers to the functions in the loadable module.
+The interface will be explained below.
+
+@item int __min_needed_from
+@itemx int __max_needed_from
+@itemx int __min_needed_to
+@itemx int __max_needed_to;
+These values have to be supplied in the init function of the module. The
+@code{__min_needed_from} value specifies how many bytes a character of
+the source character set at least needs. The @code{__max_needed_from}
+specifies the maximum value that also includes possible shift sequences.
+
+The @code{__min_needed_to} and @code{__max_needed_to} values serve the
+same purpose as @code{__min_needed_from} and @code{__max_needed_from} but
+this time for the destination character set.
+
+It is crucial that these values be accurate since otherwise the
+conversion functions will have problems or not work at all.
+
+@item int __stateful
+This element must also be initialized by the init function.
+@code{int __stateful} is nonzero if the source character set is stateful.
+Otherwise it is zero.
+
+@item void *__data
+This element can be used freely by the conversion functions in the
+module. @code{void *__data} can be used to communicate extra information
+from one call to another. @code{void *__data} need not be initialized if
+not needed at all. If @code{void *__data} element is assigned a pointer
+to dynamically allocated memory (presumably in the init function) it has
+to be made sure that the end function deallocates the memory. Otherwise
+the application will leak memory.
+
+It is important to be aware that this data structure is shared by all
+users of this specification conversion and therefore the @code{__data}
+element must not contain data specific to one specific use of the
+conversion function.
+@end table
+@end deftp
+
+@comment gconv.h
+@comment GNU
+@deftp {Data type} {struct __gconv_step_data}
+This is the data structure that contains the information specific to
+each use of the conversion functions.
+
+
+@table @code
+@item char *__outbuf
+@itemx char *__outbufend
+These elements specify the output buffer for the conversion step. The
+@code{__outbuf} element points to the beginning of the buffer, and
+@code{__outbufend} points to the byte following the last byte in the
+buffer. The conversion function must not assume anything about the size
+of the buffer but it can be safely assumed the there is room for at
+least one complete character in the output buffer.
+
+Once the conversion is finished, if the conversion is the last step, the
+@code{__outbuf} element must be modified to point after the last byte
+written into the buffer to signal how much output is available. If this
+conversion step is not the last one, the element must not be modified.
+The @code{__outbufend} element must not be modified.
+
+@item int __is_last
+This element is nonzero if this conversion step is the last one. This
+information is necessary for the recursion. See the description of the
+conversion function internals below. This element must never be
+modified.
+
+@item int __invocation_counter
+The conversion function can use this element to see how many calls of
+the conversion function already happened. Some character sets require a
+certain prolog when generating output, and by comparing this value with
+zero, one can find out whether it is the first call and whether,
+therefore, the prolog should be emitted. This element must never be
+modified.
+
+@item int __internal_use
+This element is another one rarely used but needed in certain
+situations. It is assigned a nonzero value in case the conversion
+functions are used to implement @code{mbsrtowcs} et.al.@: (i.e., the
+function is not used directly through the @code{iconv} interface).
+
+This sometimes makes a difference as it is expected that the
+@code{iconv} functions are used to translate entire texts while the
+@code{mbsrtowcs} functions are normally used only to convert single
+strings and might be used multiple times to convert entire texts.
+
+But in this situation we would have problem complying with some rules of
+the character set specification. Some character sets require a prolog,
+which must appear exactly once for an entire text. If a number of
+@code{mbsrtowcs} calls are used to convert the text, only the first call
+must add the prolog. However, because there is no communication between the
+different calls of @code{mbsrtowcs}, the conversion functions have no
+possibility to find this out. The situation is different for sequences
+of @code{iconv} calls since the handle allows access to the needed
+information.
+
+The @code{int __internal_use} element is mostly used together with
+@code{__invocation_counter} as follows:
+
+@smallexample
+if (!data->__internal_use
+ && data->__invocation_counter == 0)
+ /* @r{Emit prolog.} */
+ @dots{}
+@end smallexample
+
+This element must never be modified.
+
+@item mbstate_t *__statep
+The @code{__statep} element points to an object of type @code{mbstate_t}
+(@pxref{Keeping the state}). The conversion of a stateful character
+set must use the object pointed to by @code{__statep} to store
+information about the conversion state. The @code{__statep} element
+itself must never be modified.
+
+@item mbstate_t __state
+This element must @emph{never} be used directly. It is only part of
+this structure to have the needed space allocated.
+@end table
+@end deftp
+
+@subsubsection @code{iconv} module interfaces
+
+With the knowledge about the data structures we now can describe the
+conversion function itself. To understand the interface a bit of
+knowledge is necessary about the functionality in the C library that
+loads the objects with the conversions.
+
+It is often the case that one conversion is used more than once (i.e.,
+there are several @code{iconv_open} calls for the same set of character
+sets during one program run). The @code{mbsrtowcs} et.al.@: functions in
+the GNU C library also use the @code{iconv} functionality, which
+increases the number of uses of the same functions even more.
+
+Because of this multiple use of conversions, the modules do not get
+loaded exclusively for one conversion. Instead a module once loaded can
+be used by an arbitrary number of @code{iconv} or @code{mbsrtowcs} calls
+at the same time. The splitting of the information between conversion-
+function-specific information and conversion data makes this possible.
+The last section showed the two data structures used to do this.
+
+This is of course also reflected in the interface and semantics of the
+functions that the modules must provide. There are three functions that
+must have the following names:
+
+@table @code
+@item gconv_init
+The @code{gconv_init} function initializes the conversion function
+specific data structure. This very same object is shared by all
+conversions that use this conversion and, therefore, no state information
+about the conversion itself must be stored in here. If a module
+implements more than one conversion, the @code{gconv_init} function will
+be called multiple times.
+
+@item gconv_end
+The @code{gconv_end} function is responsible for freeing all resources
+allocated by the @code{gconv_init} function. If there is nothing to do,
+this function can be missing. Special care must be taken if the module
+implements more than one conversion and the @code{gconv_init} function
+does not allocate the same resources for all conversions.
+
+@item gconv
+This is the actual conversion function. It is called to convert one
+block of text. It gets passed the conversion step information
+initialized by @code{gconv_init} and the conversion data, specific to
+this use of the conversion functions.
+@end table
+
+There are three data types defined for the three module interface
+functions and these define the interface.
+
+@comment gconv.h
+@comment GNU
+@deftypevr {Data type} int {(*__gconv_init_fct)} (struct __gconv_step *)
+This specifies the interface of the initialization function of the
+module. It is called exactly once for each conversion the module
+implements.
+
+As explained in the description of the @code{struct __gconv_step} data
+structure above the initialization function has to initialize parts of
+it.
+
+@table @code
+@item __min_needed_from
+@itemx __max_needed_from
+@itemx __min_needed_to
+@itemx __max_needed_to
+These elements must be initialized to the exact numbers of the minimum
+and maximum number of bytes used by one character in the source and
+destination character sets, respectively. If the characters all have the
+same size, the minimum and maximum values are the same.
+
+@item __stateful
+This element must be initialized to an nonzero value if the source
+character set is stateful. Otherwise it must be zero.
+@end table
+
+If the initialization function needs to communicate some information
+to the conversion function, this communication can happen using the
+@code{__data} element of the @code{__gconv_step} structure. But since
+this data is shared by all the conversions, it must not be modified by
+the conversion function. The example below shows how this can be used.
+
+@smallexample
+#define MIN_NEEDED_FROM 1
+#define MAX_NEEDED_FROM 4
+#define MIN_NEEDED_TO 4
+#define MAX_NEEDED_TO 4
+
+int
+gconv_init (struct __gconv_step *step)
+@{
+ /* @r{Determine which direction.} */
+ struct iso2022jp_data *new_data;
+ enum direction dir = illegal_dir;
+ enum variant var = illegal_var;
+ int result;
+
+ if (__strcasecmp (step->__from_name, "ISO-2022-JP//") == 0)
+ @{
+ dir = from_iso2022jp;
+ var = iso2022jp;
+ @}
+ else if (__strcasecmp (step->__to_name, "ISO-2022-JP//") == 0)
+ @{
+ dir = to_iso2022jp;
+ var = iso2022jp;
+ @}
+ else if (__strcasecmp (step->__from_name, "ISO-2022-JP-2//") == 0)
+ @{
+ dir = from_iso2022jp;
+ var = iso2022jp2;
+ @}
+ else if (__strcasecmp (step->__to_name, "ISO-2022-JP-2//") == 0)
+ @{
+ dir = to_iso2022jp;
+ var = iso2022jp2;
+ @}
+
+ result = __GCONV_NOCONV;
+ if (dir != illegal_dir)
+ @{
+ new_data = (struct iso2022jp_data *)
+ malloc (sizeof (struct iso2022jp_data));
+
+ result = __GCONV_NOMEM;
+ if (new_data != NULL)
+ @{
+ new_data->dir = dir;
+ new_data->var = var;
+ step->__data = new_data;
+
+ if (dir == from_iso2022jp)
+ @{
+ step->__min_needed_from = MIN_NEEDED_FROM;
+ step->__max_needed_from = MAX_NEEDED_FROM;
+ step->__min_needed_to = MIN_NEEDED_TO;
+ step->__max_needed_to = MAX_NEEDED_TO;
+ @}
+ else
+ @{
+ step->__min_needed_from = MIN_NEEDED_TO;
+ step->__max_needed_from = MAX_NEEDED_TO;
+ step->__min_needed_to = MIN_NEEDED_FROM;
+ step->__max_needed_to = MAX_NEEDED_FROM + 2;
+ @}
+
+ /* @r{Yes, this is a stateful encoding.} */
+ step->__stateful = 1;
+
+ result = __GCONV_OK;
+ @}
+ @}
+
+ return result;
+@}
+@end smallexample
+
+The function first checks which conversion is wanted. The module from
+which this function is taken implements four different conversions;
+which one is selected can be determined by comparing the names. The
+comparison should always be done without paying attention to the case.
+
+Next, a data structure, which contains the necessary information about
+which conversion is selected, is allocated. The data structure
+@code{struct iso2022jp_data} is locally defined since, outside the
+module, this data is not used at all. Please note that if all four
+conversions this modules supports are requested there are four data
+blocks.
+
+One interesting thing is the initialization of the @code{__min_} and
+@code{__max_} elements of the step data object. A single ISO-2022-JP
+character can consist of one to four bytes. Therefore the
+@code{MIN_NEEDED_FROM} and @code{MAX_NEEDED_FROM} macros are defined
+this way. The output is always the @code{INTERNAL} character set (aka
+UCS-4) and therefore each character consists of exactly four bytes. For
+the conversion from @code{INTERNAL} to ISO-2022-JP we have to take into
+account that escape sequences might be necessary to switch the character
+sets. Therefore the @code{__max_needed_to} element for this direction
+gets assigned @code{MAX_NEEDED_FROM + 2}. This takes into account the
+two bytes needed for the escape sequences to single the switching. The
+asymmetry in the maximum values for the two directions can be explained
+easily: when reading ISO-2022-JP text, escape sequences can be handled
+alone (i.e., it is not necessary to process a real character since the
+effect of the escape sequence can be recorded in the state information).
+The situation is different for the other direction. Since it is in
+general not known which character comes next, one cannot emit escape
+sequences to change the state in advance. This means the escape
+sequences that have to be emitted together with the next character.
+Therefore one needs more room than only for the character itself.
+
+The possible return values of the initialization function are:
+
+@table @code
+@item __GCONV_OK
+The initialization succeeded
+@item __GCONV_NOCONV
+The requested conversion is not supported in the module. This can
+happen if the @file{gconv-modules} file has errors.
+@item __GCONV_NOMEM
+Memory required to store additional information could not be allocated.
+@end table
+@end deftypevr
+
+The function called before the module is unloaded is significantly
+easier. It often has nothing at all to do; in which case it can be left
+out completely.
+
+@comment gconv.h
+@comment GNU
+@deftypevr {Data type} void {(*__gconv_end_fct)} (struct gconv_step *)
+The task of this function is to free all resources allocated in the
+initialization function. Therefore only the @code{__data} element of
+the object pointed to by the argument is of interest. Continuing the
+example from the initialization function, the finalization function
+looks like this:
+
+@smallexample
+void
+gconv_end (struct __gconv_step *data)
+@{
+ free (data->__data);
+@}
+@end smallexample
+@end deftypevr
+
+The most important function is the conversion function itself, which can
+get quite complicated for complex character sets. But since this is not
+of interest here, we will only describe a possible skeleton for the
+conversion function.
+
+@comment gconv.h
+@comment GNU
+@deftypevr {Data type} int {(*__gconv_fct)} (struct __gconv_step *, struct __gconv_step_data *, const char **, const char *, size_t *, int)
+The conversion function can be called for two basic reason: to convert
+text or to reset the state. From the description of the @code{iconv}
+function it can be seen why the flushing mode is necessary. What mode
+is selected is determined by the sixth argument, an integer. This
+argument being nonzero means that flushing is selected.
+
+Common to both modes is where the output buffer can be found. The
+information about this buffer is stored in the conversion step data. A
+pointer to this information is passed as the second argument to this
+function. The description of the @code{struct __gconv_step_data}
+structure has more information on the conversion step data.
+
+@cindex stateful
+What has to be done for flushing depends on the source character set.
+If the source character set is not stateful, nothing has to be done.
+Otherwise the function has to emit a byte sequence to bring the state
+object into the initial state. Once this all happened the other
+conversion modules in the chain of conversions have to get the same
+chance. Whether another step follows can be determined from the
+@code{__is_last} element of the step data structure to which the first
+parameter points.
+
+The more interesting mode is when actual text has to be converted. The
+first step in this case is to convert as much text as possible from the
+input buffer and store the result in the output buffer. The start of the
+input buffer is determined by the third argument, which is a pointer to a
+pointer variable referencing the beginning of the buffer. The fourth
+argument is a pointer to the byte right after the last byte in the buffer.
+
+The conversion has to be performed according to the current state if the
+character set is stateful. The state is stored in an object pointed to
+by the @code{__statep} element of the step data (second argument). Once
+either the input buffer is empty or the output buffer is full the
+conversion stops. At this point, the pointer variable referenced by the
+third parameter must point to the byte following the last processed
+byte (i.e., if all of the input is consumed, this pointer and the fourth
+parameter have the same value).
+
+What now happens depends on whether this step is the last one. If it is
+the last step, the only thing that has to be done is to update the
+@code{__outbuf} element of the step data structure to point after the
+last written byte. This update gives the caller the information on how
+much text is available in the output buffer. In addition, the variable
+pointed to by the fifth parameter, which is of type @code{size_t}, must
+be incremented by the number of characters (@emph{not bytes}) that were
+converted in a non-reversible way. Then, the function can return.
+
+In case the step is not the last one, the later conversion functions have
+to get a chance to do their work. Therefore, the appropriate conversion
+function has to be called. The information about the functions is
+stored in the conversion data structures, passed as the first parameter.
+This information and the step data are stored in arrays, so the next
+element in both cases can be found by simple pointer arithmetic:
+
+@smallexample
+int
+gconv (struct __gconv_step *step, struct __gconv_step_data *data,
+ const char **inbuf, const char *inbufend, size_t *written,
+ int do_flush)
+@{
+ struct __gconv_step *next_step = step + 1;
+ struct __gconv_step_data *next_data = data + 1;
+ @dots{}
+@end smallexample
+
+The @code{next_step} pointer references the next step information and
+@code{next_data} the next data record. The call of the next function
+therefore will look similar to this:
+
+@smallexample
+ next_step->__fct (next_step, next_data, &outerr, outbuf,
+ written, 0)
+@end smallexample
+
+But this is not yet all. Once the function call returns the conversion
+function might have some more to do. If the return value of the function
+is @code{__GCONV_EMPTY_INPUT}, more room is available in the output
+buffer. Unless the input buffer is empty the conversion, functions start
+all over again and process the rest of the input buffer. If the return
+value is not @code{__GCONV_EMPTY_INPUT}, something went wrong and we have
+to recover from this.
+
+A requirement for the conversion function is that the input buffer
+pointer (the third argument) always point to the last character that
+was put in converted form into the output buffer. This is trivially
+true after the conversion performed in the current step, but if the
+conversion functions deeper downstream stop prematurely, not all
+characters from the output buffer are consumed and, therefore, the input
+buffer pointers must be backed off to the right position.
+
+Correcting the input buffers is easy to do if the input and output
+character sets have a fixed width for all characters. In this situation
+we can compute how many characters are left in the output buffer and,
+therefore, can correct the input buffer pointer appropriately with a
+similar computation. Things are getting tricky if either character set
+has characters represented with variable length byte sequences, and it
+gets even more complicated if the conversion has to take care of the
+state. In these cases the conversion has to be performed once again, from
+the known state before the initial conversion (i.e., if necessary the
+state of the conversion has to be reset and the conversion loop has to be
+executed again). The difference now is that it is known how much input
+must be created, and the conversion can stop before converting the first
+unused character. Once this is done the input buffer pointers must be
+updated again and the function can return.
+
+One final thing should be mentioned. If it is necessary for the
+conversion to know whether it is the first invocation (in case a prolog
+has to be emitted), the conversion function should increment the
+@code{__invocation_counter} element of the step data structure just
+before returning to the caller. See the description of the @code{struct
+__gconv_step_data} structure above for more information on how this can
+be used.
+
+The return value must be one of the following values:
+
+@table @code
+@item __GCONV_EMPTY_INPUT
+All input was consumed and there is room left in the output buffer.
+@item __GCONV_FULL_OUTPUT
+No more room in the output buffer. In case this is not the last step
+this value is propagated down from the call of the next conversion
+function in the chain.
+@item __GCONV_INCOMPLETE_INPUT
+The input buffer is not entirely empty since it contains an incomplete
+character sequence.
+@end table
+
+The following example provides a framework for a conversion function.
+In case a new conversion has to be written the holes in this
+implementation have to be filled and that is it.
+
+@smallexample
+int
+gconv (struct __gconv_step *step, struct __gconv_step_data *data,
+ const char **inbuf, const char *inbufend, size_t *written,
+ int do_flush)
+@{
+ struct __gconv_step *next_step = step + 1;
+ struct __gconv_step_data *next_data = data + 1;
+ gconv_fct fct = next_step->__fct;
+ int status;
+
+ /* @r{If the function is called with no input this means we have}
+ @r{to reset to the initial state. The possibly partly}
+ @r{converted input is dropped.} */
+ if (do_flush)
+ @{
+ status = __GCONV_OK;
+
+ /* @r{Possible emit a byte sequence which put the state object}
+ @r{into the initial state.} */
+
+ /* @r{Call the steps down the chain if there are any but only}
+ @r{if we successfully emitted the escape sequence.} */
+ if (status == __GCONV_OK && ! data->__is_last)
+ status = fct (next_step, next_data, NULL, NULL,
+ written, 1);
+ @}
+ else
+ @{
+ /* @r{We preserve the initial values of the pointer variables.} */
+ const char *inptr = *inbuf;
+ char *outbuf = data->__outbuf;
+ char *outend = data->__outbufend;
+ char *outptr;
+
+ do
+ @{
+ /* @r{Remember the start value for this round.} */
+ inptr = *inbuf;
+ /* @r{The outbuf buffer is empty.} */
+ outptr = outbuf;
+
+ /* @r{For stateful encodings the state must be safe here.} */
+
+ /* @r{Run the conversion loop. @code{status} is set}
+ @r{appropriately afterwards.} */
+
+ /* @r{If this is the last step, leave the loop. There is}
+ @r{nothing we can do.} */
+ if (data->__is_last)
+ @{
+ /* @r{Store information about how many bytes are}
+ @r{available.} */
+ data->__outbuf = outbuf;
+
+ /* @r{If any non-reversible conversions were performed,}
+ @r{add the number to @code{*written}.} */
+
+ break;
+ @}
+
+ /* @r{Write out all output that was produced.} */
+ if (outbuf > outptr)
+ @{
+ const char *outerr = data->__outbuf;
+ int result;
+
+ result = fct (next_step, next_data, &outerr,
+ outbuf, written, 0);
+
+ if (result != __GCONV_EMPTY_INPUT)
+ @{
+ if (outerr != outbuf)
+ @{
+ /* @r{Reset the input buffer pointer. We}
+ @r{document here the complex case.} */
+ size_t nstatus;
+
+ /* @r{Reload the pointers.} */
+ *inbuf = inptr;
+ outbuf = outptr;
+
+ /* @r{Possibly reset the state.} */
+
+ /* @r{Redo the conversion, but this time}
+ @r{the end of the output buffer is at}
+ @r{@code{outerr}.} */
+ @}
+
+ /* @r{Change the status.} */
+ status = result;
+ @}
+ else
+ /* @r{All the output is consumed, we can make}
+ @r{ another run if everything was ok.} */
+ if (status == __GCONV_FULL_OUTPUT)
+ status = __GCONV_OK;
+ @}
+ @}
+ while (status == __GCONV_OK);
+
+ /* @r{We finished one use of this step.} */
+ ++data->__invocation_counter;
+ @}
+
+ return status;
+@}
+@end smallexample
+@end deftypevr
+
+This information should be sufficient to write new modules. Anybody
+doing so should also take a look at the available source code in the GNU
+C library sources. It contains many examples of working and optimized
+modules.
+
+@c File charset.texi edited October 2001 by Dennis Grace, IBM Corporation
Modified: glibc-doc-reference/tags/2.13-1/manual/errno.texi
===================================================================
--- glibc-doc-reference/trunk/manual/errno.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/errno.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1265,6 +1265,12 @@
@comment errno ???/???
@end deftypevr
+@comment errno.h
+@comment Linux: Operation not possible due to RF-kill
+@deftypevr Macro int ERFKILL
+@comment errno ???/???
+@end deftypevr
+
@node Error Messages, , Error Codes, Error Reporting
@section Error Messages
@@ -1419,7 +1425,7 @@
@code{perror} generates is not what is wanted and there is no way to
extend or change what @code{perror} does. The GNU coding standard, for
instance, requires error messages to be preceded by the program name and
-programs which read some input files should should provide information
+programs which read some input files should provide information
about the input file name and the line number in case an error is
encountered while reading the file. For these occasions there are two
functions available which are widely used throughout the GNU project.
Modified: glibc-doc-reference/tags/2.13-1/manual/getopt.texi
===================================================================
--- glibc-doc-reference/trunk/manual/getopt.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/getopt.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -269,7 +269,7 @@
@var{argv} of the next remaining argument.
@end deftypefun
-Since long option names were used before before the @code{getopt_long}
+Since long option names were used before the @code{getopt_long}
options was invented there are program interfaces which require programs
to recognize options like @w{@samp{-option value}} instead of
@w{@samp{--option value}}. To enable these programs to use the GNU
Modified: glibc-doc-reference/tags/2.13-1/manual/install.texi
===================================================================
--- glibc-doc-reference/trunk/manual/install.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/install.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -330,16 +330,15 @@
@item
GCC 3.4 or newer, GCC 4.1 recommended
-The GNU C library can only be compiled with the GNU C compiler family.
-For the 2.3 releases, GCC 3.2 or higher is required; GCC 3.4 is the
-compiler we advise to use for 2.3 versions.
-For the 2.4 release, GCC 3.4 or higher is required; as of this
-writing, GCC 4.1 is the compiler we advise to use for current versions.
+For the 2.4 release or later, GCC 3.4 or higher is required; as of this
+writing, GCC 4.4 is the compiler we advise to use for current versions.
On certain machines including @code{powerpc64}, compilers prior to GCC
4.0 have bugs that prevent them compiling the C library code in the
2.4 release. On other machines, GCC 4.1 is required to build the C
library with support for the correct @code{long double} type format;
-these include @code{powerpc} (32 bit), @code{s390} and @code{s390x}.
+these include @code{powerpc} (32 bit), @code{s390} and @code{s390x}. For
+other architectures special compiler-provided headers are needed
+(like @file{cpuid.h} on x86) which only come with later compiler versions.
You can use whatever compiler you like to compile programs that use GNU
libc, but be aware that both GCC 2.7 and 2.8 have bugs in their
Modified: glibc-doc-reference/tags/2.13-1/manual/libc.texinfo
===================================================================
--- glibc-doc-reference/trunk/manual/libc.texinfo 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/libc.texinfo 2011-05-02 18:20:00 UTC (rev 4639)
@@ -29,10 +29,10 @@
of @cite{The GNU C Library Reference Manual}, for version @value{VERSION}.
Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
-2003, 2007, 2008 Free Software Foundation, Inc.
+2003, 2007, 2008, 2010 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.2 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Free Software Needs Free Documentation''
and ``GNU Lesser General Public License'', the Front-Cover texts being
Deleted: glibc-doc-reference/tags/2.13-1/manual/linuxthreads.texi
===================================================================
--- glibc-doc-reference/trunk/manual/linuxthreads.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/linuxthreads.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,1627 +0,0 @@
-@node POSIX Threads
-@c @node POSIX Threads, , Top, Top
-@chapter POSIX Threads
-@c %MENU% The standard threads library
-
-@c This chapter needs more work bigtime. -zw
-
-This chapter describes the pthreads (POSIX threads) library. This
-library provides support functions for multithreaded programs: thread
-primitives, synchronization objects, and so forth. It also implements
-POSIX 1003.1b semaphores (not to be confused with System V semaphores).
-
-The threads operations (@samp{pthread_*}) do not use @var{errno}.
-Instead they return an error code directly. The semaphore operations do
-use @var{errno}.
-
-@menu
-* Basic Thread Operations:: Creating, terminating, and waiting for threads.
-* Thread Attributes:: Tuning thread scheduling.
-* Cancellation:: Stopping a thread before it's done.
-* Cleanup Handlers:: Deallocating resources when a thread is
- canceled.
-* Mutexes:: One way to synchronize threads.
-* Condition Variables:: Another way.
-* POSIX Semaphores:: And a third way.
-* Thread-Specific Data:: Variables with different values in
- different threads.
-* Threads and Signal Handling:: Why you should avoid mixing the two, and
- how to do it if you must.
-* Threads and Fork:: Interactions between threads and the
- @code{fork} function.
-* Streams and Fork:: Interactions between stdio streams and
- @code{fork}.
-* Miscellaneous Thread Functions:: A grab bag of utility routines.
-@end menu
-
-@node Basic Thread Operations
-@section Basic Thread Operations
-
-These functions are the thread equivalents of @code{fork}, @code{exit},
-and @code{wait}.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_create (pthread_t * @var{thread}, pthread_attr_t * @var{attr}, void * (*@var{start_routine})(void *), void * @var{arg})
-@code{pthread_create} creates a new thread of control that executes
-concurrently with the calling thread. The new thread calls the
-function @var{start_routine}, passing it @var{arg} as first argument. The
-new thread terminates either explicitly, by calling @code{pthread_exit},
-or implicitly, by returning from the @var{start_routine} function. The
-latter case is equivalent to calling @code{pthread_exit} with the result
-returned by @var{start_routine} as exit code.
-
-The @var{attr} argument specifies thread attributes to be applied to the
-new thread. @xref{Thread Attributes}, for details. The @var{attr}
-argument can also be @code{NULL}, in which case default attributes are
-used: the created thread is joinable (not detached) and has an ordinary
-(not realtime) scheduling policy.
-
-On success, the identifier of the newly created thread is stored in the
-location pointed by the @var{thread} argument, and a 0 is returned. On
-error, a non-zero error code is returned.
-
-This function may return the following errors:
-@table @code
-@item EAGAIN
-Not enough system resources to create a process for the new thread,
-or more than @code{PTHREAD_THREADS_MAX} threads are already active.
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_exit (void *@var{retval})
-@code{pthread_exit} terminates the execution of the calling thread. All
-cleanup handlers (@pxref{Cleanup Handlers}) that have been set for the
-calling thread with @code{pthread_cleanup_push} are executed in reverse
-order (the most recently pushed handler is executed first). Finalization
-functions for thread-specific data are then called for all keys that
-have non-@code{NULL} values associated with them in the calling thread
-(@pxref{Thread-Specific Data}). Finally, execution of the calling
-thread is stopped.
-
-The @var{retval} argument is the return value of the thread. It can be
-retrieved from another thread using @code{pthread_join}.
-
-The @code{pthread_exit} function never returns.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cancel (pthread_t @var{thread})
-
-@code{pthread_cancel} sends a cancellation request to the thread denoted
-by the @var{thread} argument. If there is no such thread,
-@code{pthread_cancel} fails and returns @code{ESRCH}. Otherwise it
-returns 0. @xref{Cancellation}, for details.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_join (pthread_t @var{th}, void **thread_@var{return})
-@code{pthread_join} suspends the execution of the calling thread until
-the thread identified by @var{th} terminates, either by calling
-@code{pthread_exit} or by being canceled.
-
-If @var{thread_return} is not @code{NULL}, the return value of @var{th}
-is stored in the location pointed to by @var{thread_return}. The return
-value of @var{th} is either the argument it gave to @code{pthread_exit},
-or @code{PTHREAD_CANCELED} if @var{th} was canceled.
-
-The joined thread @code{th} must be in the joinable state: it must not
-have been detached using @code{pthread_detach} or the
-@code{PTHREAD_CREATE_DETACHED} attribute to @code{pthread_create}.
-
-When a joinable thread terminates, its memory resources (thread
-descriptor and stack) are not deallocated until another thread performs
-@code{pthread_join} on it. Therefore, @code{pthread_join} must be called
-once for each joinable thread created to avoid memory leaks.
-
-At most one thread can wait for the termination of a given
-thread. Calling @code{pthread_join} on a thread @var{th} on which
-another thread is already waiting for termination returns an error.
-
-@code{pthread_join} is a cancellation point. If a thread is canceled
-while suspended in @code{pthread_join}, the thread execution resumes
-immediately and the cancellation is executed without waiting for the
-@var{th} thread to terminate. If cancellation occurs during
-@code{pthread_join}, the @var{th} thread remains not joined.
-
-On success, the return value of @var{th} is stored in the location
-pointed to by @var{thread_return}, and 0 is returned. On error, one of
-the following values is returned:
-@table @code
-@item ESRCH
-No thread could be found corresponding to that specified by @var{th}.
-@item EINVAL
-The @var{th} thread has been detached, or another thread is already
-waiting on termination of @var{th}.
-@item EDEADLK
-The @var{th} argument refers to the calling thread.
-@end table
-@end deftypefun
-
-@node Thread Attributes
-@section Thread Attributes
-
-@comment pthread.h
-@comment POSIX
-
-Threads have a number of attributes that may be set at creation time.
-This is done by filling a thread attribute object @var{attr} of type
-@code{pthread_attr_t}, then passing it as second argument to
-@code{pthread_create}. Passing @code{NULL} is equivalent to passing a
-thread attribute object with all attributes set to their default values.
-
-Attribute objects are consulted only when creating a new thread. The
-same attribute object can be used for creating several threads.
-Modifying an attribute object after a call to @code{pthread_create} does
-not change the attributes of the thread previously created.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_init (pthread_attr_t *@var{attr})
-@code{pthread_attr_init} initializes the thread attribute object
-@var{attr} and fills it with default values for the attributes. (The
-default values are listed below for each attribute.)
-
-Each attribute @var{attrname} (see below for a list of all attributes)
-can be individually set using the function
-@code{pthread_attr_set@var{attrname}} and retrieved using the function
-@code{pthread_attr_get@var{attrname}}.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_destroy (pthread_attr_t *@var{attr})
-@code{pthread_attr_destroy} destroys the attribute object pointed to by
-@var{attr} releasing any resources associated with it. @var{attr} is
-left in an undefined state, and you must not use it again in a call to
-any pthreads function until it has been reinitialized.
-@end deftypefun
-
-@findex pthread_attr_setdetachstate
-@findex pthread_attr_setguardsize
-@findex pthread_attr_setinheritsched
-@findex pthread_attr_setschedparam
-@findex pthread_attr_setschedpolicy
-@findex pthread_attr_setscope
-@findex pthread_attr_setstack
-@findex pthread_attr_setstackaddr
-@findex pthread_attr_setstacksize
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_setattr (pthread_attr_t *@var{obj}, int @var{value})
-Set attribute @var{attr} to @var{value} in the attribute object pointed
-to by @var{obj}. See below for a list of possible attributes and the
-values they can take.
-
-On success, these functions return 0. If @var{value} is not meaningful
-for the @var{attr} being modified, they will return the error code
-@code{EINVAL}. Some of the functions have other failure modes; see
-below.
-@end deftypefun
-
-@findex pthread_attr_getdetachstate
-@findex pthread_attr_getguardsize
-@findex pthread_attr_getinheritsched
-@findex pthread_attr_getschedparam
-@findex pthread_attr_getschedpolicy
-@findex pthread_attr_getscope
-@findex pthread_attr_getstack
-@findex pthread_attr_getstackaddr
-@findex pthread_attr_getstacksize
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_getattr (const pthread_attr_t *@var{obj}, int *@var{value})
-Store the current setting of @var{attr} in @var{obj} into the variable
-pointed to by @var{value}.
-
-These functions always return 0.
-@end deftypefun
-
-The following thread attributes are supported:
-@table @samp
-@item detachstate
-Choose whether the thread is created in the joinable state (value
-@code{PTHREAD_CREATE_JOINABLE}) or in the detached state
-(@code{PTHREAD_CREATE_DETACHED}). The default is
-@code{PTHREAD_CREATE_JOINABLE}.
-
-In the joinable state, another thread can synchronize on the thread
-termination and recover its termination code using @code{pthread_join},
-but some of the thread resources are kept allocated after the thread
-terminates, and reclaimed only when another thread performs
-@code{pthread_join} on that thread.
-
-In the detached state, the thread resources are immediately freed when
-it terminates, but @code{pthread_join} cannot be used to synchronize on
-the thread termination.
-
-A thread created in the joinable state can later be put in the detached
-thread using @code{pthread_detach}.
-
-@item schedpolicy
-Select the scheduling policy for the thread: one of @code{SCHED_OTHER}
-(regular, non-realtime scheduling), @code{SCHED_RR} (realtime,
-round-robin) or @code{SCHED_FIFO} (realtime, first-in first-out).
-The default is @code{SCHED_OTHER}.
-@c Not doc'd in our manual: FIXME.
-@c See @code{sched_setpolicy} for more information on scheduling policies.
-
-The realtime scheduling policies @code{SCHED_RR} and @code{SCHED_FIFO}
-are available only to processes with superuser privileges.
-@code{pthread_attr_setschedparam} will fail and return @code{ENOTSUP} if
-you try to set a realtime policy when you are unprivileged.
-
-The scheduling policy of a thread can be changed after creation with
-@code{pthread_setschedparam}.
-
-@item schedparam
-Change the scheduling parameter (the scheduling priority)
-for the thread. The default is 0.
-
-This attribute is not significant if the scheduling policy is
-@code{SCHED_OTHER}; it only matters for the realtime policies
-@code{SCHED_RR} and @code{SCHED_FIFO}.
-
-The scheduling priority of a thread can be changed after creation with
-@code{pthread_setschedparam}.
-
-@item inheritsched
-Choose whether the scheduling policy and scheduling parameter for the
-newly created thread are determined by the values of the
-@var{schedpolicy} and @var{schedparam} attributes (value
-@code{PTHREAD_EXPLICIT_SCHED}) or are inherited from the parent thread
-(value @code{PTHREAD_INHERIT_SCHED}). The default is
-@code{PTHREAD_EXPLICIT_SCHED}.
-
-@item scope
-Choose the scheduling contention scope for the created thread. The
-default is @code{PTHREAD_SCOPE_SYSTEM}, meaning that the threads contend
-for CPU time with all processes running on the machine. In particular,
-thread priorities are interpreted relative to the priorities of all
-other processes on the machine. The other possibility,
-@code{PTHREAD_SCOPE_PROCESS}, means that scheduling contention occurs
-only between the threads of the running process: thread priorities are
-interpreted relative to the priorities of the other threads of the
-process, regardless of the priorities of other processes.
-
-@code{PTHREAD_SCOPE_PROCESS} is not supported in LinuxThreads. If you
-try to set the scope to this value, @code{pthread_attr_setscope} will
-fail and return @code{ENOTSUP}.
-
-@item stackaddr
-Provide an address for an application managed stack. The size of the
-stack must be at least @code{PTHREAD_STACK_MIN}.
-
-@item stacksize
-Change the size of the stack created for the thread. The value defines
-the minimum stack size, in bytes.
-
-If the value exceeds the system's maximum stack size, or is smaller
-than @code{PTHREAD_STACK_MIN}, @code{pthread_attr_setstacksize} will
-fail and return @code{EINVAL}.
-
-@item stack
-Provide both the address and size of an application managed stack to
-use for the new thread. The base of the memory area is @var{stackaddr}
-with the size of the memory area, @var{stacksize}, measured in bytes.
-
-If the value of @var{stacksize} is less than @code{PTHREAD_STACK_MIN},
-or greater than the system's maximum stack size, or if the value of
-@var{stackaddr} lacks the proper alignment, @code{pthread_attr_setstack}
-will fail and return @code{EINVAL}.
-
-@item guardsize
-Change the minimum size in bytes of the guard area for the thread's
-stack. The default size is a single page. If this value is set, it
-will be rounded up to the nearest page size. If the value is set to 0,
-a guard area will not be created for this thread. The space allocated
-for the guard area is used to catch stack overflow. Therefore, when
-allocating large structures on the stack, a larger guard area may be
-required to catch a stack overflow.
-
-If the caller is managing their own stacks (if the @code{stackaddr}
-attribute has been set), then the @code{guardsize} attribute is ignored.
-
-If the value exceeds the @code{stacksize}, @code{pthread_atrr_setguardsize}
-will fail and return @code{EINVAL}.
-@end table
-
-@node Cancellation
-@section Cancellation
-
-Cancellation is the mechanism by which a thread can terminate the
-execution of another thread. More precisely, a thread can send a
-cancellation request to another thread. Depending on its settings, the
-target thread can then either ignore the request, honor it immediately,
-or defer it till it reaches a cancellation point. When threads are
-first created by @code{pthread_create}, they always defer cancellation
-requests.
-
-When a thread eventually honors a cancellation request, it behaves as if
-@code{pthread_exit(PTHREAD_CANCELED)} was called. All cleanup handlers
-are executed in reverse order, finalization functions for
-thread-specific data are called, and finally the thread stops executing.
-If the canceled thread was joinable, the return value
-@code{PTHREAD_CANCELED} is provided to whichever thread calls
-@var{pthread_join} on it. See @code{pthread_exit} for more information.
-
-Cancellation points are the points where the thread checks for pending
-cancellation requests and performs them. The POSIX threads functions
-@code{pthread_join}, @code{pthread_cond_wait},
-@code{pthread_cond_timedwait}, @code{pthread_testcancel},
-@code{sem_wait}, and @code{sigwait} are cancellation points. In
-addition, these system calls are cancellation points:
-
-@multitable @columnfractions .33 .33 .33
-@item @t{accept} @tab @t{open} @tab @t{sendmsg}
-@item @t{close} @tab @t{pause} @tab @t{sendto}
-@item @t{connect} @tab @t{read} @tab @t{system}
-@item @t{fcntl} @tab @t{recv} @tab @t{tcdrain}
-@item @t{fsync} @tab @t{recvfrom} @tab @t{wait}
-@item @t{lseek} @tab @t{recvmsg} @tab @t{waitpid}
-@item @t{msync} @tab @t{send} @tab @t{write}
-@item @t{nanosleep}
-@end multitable
-
-@noindent
-All library functions that call these functions (such as
-@code{printf}) are also cancellation points.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setcancelstate (int @var{state}, int *@var{oldstate})
-@code{pthread_setcancelstate} changes the cancellation state for the
-calling thread -- that is, whether cancellation requests are ignored or
-not. The @var{state} argument is the new cancellation state: either
-@code{PTHREAD_CANCEL_ENABLE} to enable cancellation, or
-@code{PTHREAD_CANCEL_DISABLE} to disable cancellation (cancellation
-requests are ignored).
-
-If @var{oldstate} is not @code{NULL}, the previous cancellation state is
-stored in the location pointed to by @var{oldstate}, and can thus be
-restored later by another call to @code{pthread_setcancelstate}.
-
-If the @var{state} argument is not @code{PTHREAD_CANCEL_ENABLE} or
-@code{PTHREAD_CANCEL_DISABLE}, @code{pthread_setcancelstate} fails and
-returns @code{EINVAL}. Otherwise it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setcanceltype (int @var{type}, int *@var{oldtype})
-@code{pthread_setcanceltype} changes the type of responses to
-cancellation requests for the calling thread: asynchronous (immediate)
-or deferred. The @var{type} argument is the new cancellation type:
-either @code{PTHREAD_CANCEL_ASYNCHRONOUS} to cancel the calling thread
-as soon as the cancellation request is received, or
-@code{PTHREAD_CANCEL_DEFERRED} to keep the cancellation request pending
-until the next cancellation point. If @var{oldtype} is not @code{NULL},
-the previous cancellation state is stored in the location pointed to by
-@var{oldtype}, and can thus be restored later by another call to
-@code{pthread_setcanceltype}.
-
-If the @var{type} argument is not @code{PTHREAD_CANCEL_DEFERRED} or
-@code{PTHREAD_CANCEL_ASYNCHRONOUS}, @code{pthread_setcanceltype} fails
-and returns @code{EINVAL}. Otherwise it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_testcancel (@var{void})
-@code{pthread_testcancel} does nothing except testing for pending
-cancellation and executing it. Its purpose is to introduce explicit
-checks for cancellation in long sequences of code that do not call
-cancellation point functions otherwise.
-@end deftypefun
-
-@node Cleanup Handlers
-@section Cleanup Handlers
-
-Cleanup handlers are functions that get called when a thread terminates,
-either by calling @code{pthread_exit} or because of
-cancellation. Cleanup handlers are installed and removed following a
-stack-like discipline.
-
-The purpose of cleanup handlers is to free the resources that a thread
-may hold at the time it terminates. In particular, if a thread exits or
-is canceled while it owns a locked mutex, the mutex will remain locked
-forever and prevent other threads from executing normally. The best way
-to avoid this is, just before locking the mutex, to install a cleanup
-handler whose effect is to unlock the mutex. Cleanup handlers can be
-used similarly to free blocks allocated with @code{malloc} or close file
-descriptors on thread termination.
-
-Here is how to lock a mutex @var{mut} in such a way that it will be
-unlocked if the thread is canceled while @var{mut} is locked:
-
-@smallexample
-pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_mutex_unlock(&mut);
-pthread_cleanup_pop(0);
-@end smallexample
-
-Equivalently, the last two lines can be replaced by
-
-@smallexample
-pthread_cleanup_pop(1);
-@end smallexample
-
-Notice that the code above is safe only in deferred cancellation mode
-(see @code{pthread_setcanceltype}). In asynchronous cancellation mode, a
-cancellation can occur between @code{pthread_cleanup_push} and
-@code{pthread_mutex_lock}, or between @code{pthread_mutex_unlock} and
-@code{pthread_cleanup_pop}, resulting in both cases in the thread trying
-to unlock a mutex not locked by the current thread. This is the main
-reason why asynchronous cancellation is difficult to use.
-
-If the code above must also work in asynchronous cancellation mode,
-then it must switch to deferred mode for locking and unlocking the
-mutex:
-
-@smallexample
-pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
-pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_cleanup_pop(1);
-pthread_setcanceltype(oldtype, NULL);
-@end smallexample
-
-The code above can be rewritten in a more compact and efficient way,
-using the non-portable functions @code{pthread_cleanup_push_defer_np}
-and @code{pthread_cleanup_pop_restore_np}:
-
-@smallexample
-pthread_cleanup_push_defer_np(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_cleanup_pop_restore_np(1);
-@end smallexample
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_cleanup_push (void (*@var{routine}) (void *), void *@var{arg})
-
-@code{pthread_cleanup_push} installs the @var{routine} function with
-argument @var{arg} as a cleanup handler. From this point on to the
-matching @code{pthread_cleanup_pop}, the function @var{routine} will be
-called with arguments @var{arg} when the thread terminates, either
-through @code{pthread_exit} or by cancellation. If several cleanup
-handlers are active at that point, they are called in LIFO order: the
-most recently installed handler is called first.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_cleanup_pop (int @var{execute})
-@code{pthread_cleanup_pop} removes the most recently installed cleanup
-handler. If the @var{execute} argument is not 0, it also executes the
-handler, by calling the @var{routine} function with arguments
-@var{arg}. If the @var{execute} argument is 0, the handler is only
-removed but not executed.
-@end deftypefun
-
-Matching pairs of @code{pthread_cleanup_push} and
-@code{pthread_cleanup_pop} must occur in the same function, at the same
-level of block nesting. Actually, @code{pthread_cleanup_push} and
-@code{pthread_cleanup_pop} are macros, and the expansion of
-@code{pthread_cleanup_push} introduces an open brace @code{@{} with the
-matching closing brace @code{@}} being introduced by the expansion of the
-matching @code{pthread_cleanup_pop}.
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_cleanup_push_defer_np (void (*@var{routine}) (void *), void *@var{arg})
-@code{pthread_cleanup_push_defer_np} is a non-portable extension that
-combines @code{pthread_cleanup_push} and @code{pthread_setcanceltype}.
-It pushes a cleanup handler just as @code{pthread_cleanup_push} does,
-but also saves the current cancellation type and sets it to deferred
-cancellation. This ensures that the cleanup mechanism is effective even
-if the thread was initially in asynchronous cancellation mode.
-@end deftypefun
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_cleanup_pop_restore_np (int @var{execute})
-@code{pthread_cleanup_pop_restore_np} pops a cleanup handler introduced
-by @code{pthread_cleanup_push_defer_np}, and restores the cancellation
-type to its value at the time @code{pthread_cleanup_push_defer_np} was
-called.
-@end deftypefun
-
-@code{pthread_cleanup_push_defer_np} and
-@code{pthread_cleanup_pop_restore_np} must occur in matching pairs, at
-the same level of block nesting.
-
-The sequence
-
-@smallexample
-pthread_cleanup_push_defer_np(routine, arg);
-...
-pthread_cleanup_pop_restore_np(execute);
-@end smallexample
-
-@noindent
-is functionally equivalent to (but more compact and efficient than)
-
-@smallexample
-@{
- int oldtype;
- pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
- pthread_cleanup_push(routine, arg);
- ...
- pthread_cleanup_pop(execute);
- pthread_setcanceltype(oldtype, NULL);
-@}
-@end smallexample
-
-
-@node Mutexes
-@section Mutexes
-
-A mutex is a MUTual EXclusion device, and is useful for protecting
-shared data structures from concurrent modifications, and implementing
-critical sections and monitors.
-
-A mutex has two possible states: unlocked (not owned by any thread),
-and locked (owned by one thread). A mutex can never be owned by two
-different threads simultaneously. A thread attempting to lock a mutex
-that is already locked by another thread is suspended until the owning
-thread unlocks the mutex first.
-
-None of the mutex functions is a cancellation point, not even
-@code{pthread_mutex_lock}, in spite of the fact that it can suspend a
-thread for arbitrary durations. This way, the status of mutexes at
-cancellation points is predictable, allowing cancellation handlers to
-unlock precisely those mutexes that need to be unlocked before the
-thread stops executing. Consequently, threads using deferred
-cancellation should never hold a mutex for extended periods of time.
-
-It is not safe to call mutex functions from a signal handler. In
-particular, calling @code{pthread_mutex_lock} or
-@code{pthread_mutex_unlock} from a signal handler may deadlock the
-calling thread.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_init (pthread_mutex_t *@var{mutex}, const pthread_mutexattr_t *@var{mutexattr})
-
-@code{pthread_mutex_init} initializes the mutex object pointed to by
-@var{mutex} according to the mutex attributes specified in @var{mutexattr}.
-If @var{mutexattr} is @code{NULL}, default attributes are used instead.
-
-The LinuxThreads implementation supports only one mutex attribute,
-the @var{mutex type}, which is either ``fast'', ``recursive'', or
-``error checking''. The type of a mutex determines whether
-it can be locked again by a thread that already owns it.
-The default type is ``fast''.
-
-Variables of type @code{pthread_mutex_t} can also be initialized
-statically, using the constants @code{PTHREAD_MUTEX_INITIALIZER} (for
-timed mutexes), @code{PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP} (for
-recursive mutexes), @code{PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP}
-(for fast mutexes(, and @code{PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP}
-(for error checking mutexes).
-
-@code{pthread_mutex_init} always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_lock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_lock} locks the given mutex. If the mutex is
-currently unlocked, it becomes locked and owned by the calling thread,
-and @code{pthread_mutex_lock} returns immediately. If the mutex is
-already locked by another thread, @code{pthread_mutex_lock} suspends the
-calling thread until the mutex is unlocked.
-
-If the mutex is already locked by the calling thread, the behavior of
-@code{pthread_mutex_lock} depends on the type of the mutex. If the mutex
-is of the ``fast'' type, the calling thread is suspended. It will
-remain suspended forever, because no other thread can unlock the mutex.
-If the mutex is of the ``error checking'' type, @code{pthread_mutex_lock}
-returns immediately with the error code @code{EDEADLK}. If the mutex is
-of the ``recursive'' type, @code{pthread_mutex_lock} succeeds and
-returns immediately, recording the number of times the calling thread
-has locked the mutex. An equal number of @code{pthread_mutex_unlock}
-operations must be performed before the mutex returns to the unlocked
-state.
-@c This doesn't discuss PTHREAD_MUTEX_TIMED_NP mutex attributes. FIXME
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_trylock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_trylock} behaves identically to
-@code{pthread_mutex_lock}, except that it does not block the calling
-thread if the mutex is already locked by another thread (or by the
-calling thread in the case of a ``fast'' mutex). Instead,
-@code{pthread_mutex_trylock} returns immediately with the error code
-@code{EBUSY}.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_timedlock (pthread_mutex_t *@var{mutex}, const struct timespec *@var{abstime})
-The @code{pthread_mutex_timedlock} is similar to the
-@code{pthread_mutex_lock} function but instead of blocking for in
-indefinite time if the mutex is locked by another thread, it returns
-when the time specified in @var{abstime} is reached.
-
-This function can only be used on standard (``timed'') and ``error
-checking'' mutexes. It behaves just like @code{pthread_mutex_lock} for
-all other types.
-
-If the mutex is successfully locked, the function returns zero. If the
-time specified in @var{abstime} is reached without the mutex being locked,
-@code{ETIMEDOUT} is returned.
-
-This function was introduced in the POSIX.1d revision of the POSIX standard.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_unlock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_unlock} unlocks the given mutex. The mutex is
-assumed to be locked and owned by the calling thread on entrance to
-@code{pthread_mutex_unlock}. If the mutex is of the ``fast'' type,
-@code{pthread_mutex_unlock} always returns it to the unlocked state. If
-it is of the ``recursive'' type, it decrements the locking count of the
-mutex (number of @code{pthread_mutex_lock} operations performed on it by
-the calling thread), and only when this count reaches zero is the mutex
-actually unlocked.
-
-On ``error checking'' mutexes, @code{pthread_mutex_unlock} actually
-checks at run-time that the mutex is locked on entrance, and that it was
-locked by the same thread that is now calling
-@code{pthread_mutex_unlock}. If these conditions are not met,
-@code{pthread_mutex_unlock} returns @code{EPERM}, and the mutex remains
-unchanged. ``Fast'' and ``recursive'' mutexes perform no such checks,
-thus allowing a locked mutex to be unlocked by a thread other than its
-owner. This is non-portable behavior and must not be relied upon.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_destroy (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_destroy} destroys a mutex object, freeing the
-resources it might hold. The mutex must be unlocked on entrance. In the
-LinuxThreads implementation, no resources are associated with mutex
-objects, thus @code{pthread_mutex_destroy} actually does nothing except
-checking that the mutex is unlocked.
-
-If the mutex is locked by some thread, @code{pthread_mutex_destroy}
-returns @code{EBUSY}. Otherwise it returns 0.
-@end deftypefun
-
-If any of the above functions (except @code{pthread_mutex_init})
-is applied to an uninitialized mutex, they will simply return
-@code{EINVAL} and do nothing.
-
-A shared global variable @var{x} can be protected by a mutex as follows:
-
-@smallexample
-int x;
-pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
-@end smallexample
-
-All accesses and modifications to @var{x} should be bracketed by calls to
-@code{pthread_mutex_lock} and @code{pthread_mutex_unlock} as follows:
-
-@smallexample
-pthread_mutex_lock(&mut);
-/* operate on x */
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Mutex attributes can be specified at mutex creation time, by passing a
-mutex attribute object as second argument to @code{pthread_mutex_init}.
-Passing @code{NULL} is equivalent to passing a mutex attribute object
-with all attributes set to their default values.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_init (pthread_mutexattr_t *@var{attr})
-@code{pthread_mutexattr_init} initializes the mutex attribute object
-@var{attr} and fills it with default values for the attributes.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_destroy (pthread_mutexattr_t *@var{attr})
-@code{pthread_mutexattr_destroy} destroys a mutex attribute object,
-which must not be reused until it is
-reinitialized. @code{pthread_mutexattr_destroy} does nothing in the
-LinuxThreads implementation.
-
-This function always returns 0.
-@end deftypefun
-
-LinuxThreads supports only one mutex attribute: the mutex type, which is
-either @code{PTHREAD_MUTEX_ADAPTIVE_NP} for ``fast'' mutexes,
-@code{PTHREAD_MUTEX_RECURSIVE_NP} for ``recursive'' mutexes,
-@code{PTHREAD_MUTEX_TIMED_NP} for ``timed'' mutexes, or
-@code{PTHREAD_MUTEX_ERRORCHECK_NP} for ``error checking'' mutexes. As
-the @code{NP} suffix indicates, this is a non-portable extension to the
-POSIX standard and should not be employed in portable programs.
-
-The mutex type determines what happens if a thread attempts to lock a
-mutex it already owns with @code{pthread_mutex_lock}. If the mutex is of
-the ``fast'' type, @code{pthread_mutex_lock} simply suspends the calling
-thread forever. If the mutex is of the ``error checking'' type,
-@code{pthread_mutex_lock} returns immediately with the error code
-@code{EDEADLK}. If the mutex is of the ``recursive'' type, the call to
-@code{pthread_mutex_lock} returns immediately with a success return
-code. The number of times the thread owning the mutex has locked it is
-recorded in the mutex. The owning thread must call
-@code{pthread_mutex_unlock} the same number of times before the mutex
-returns to the unlocked state.
-
-The default mutex type is ``timed'', that is, @code{PTHREAD_MUTEX_TIMED_NP}.
-@c This doesn't describe how a ``timed'' mutex behaves. FIXME
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_settype (pthread_mutexattr_t *@var{attr}, int @var{type})
-@code{pthread_mutexattr_settype} sets the mutex type attribute in
-@var{attr} to the value specified by @var{type}.
-
-If @var{type} is not @code{PTHREAD_MUTEX_ADAPTIVE_NP},
-@code{PTHREAD_MUTEX_RECURSIVE_NP}, @code{PTHREAD_MUTEX_TIMED_NP}, or
-@code{PTHREAD_MUTEX_ERRORCHECK_NP}, this function will return
-@code{EINVAL} and leave @var{attr} unchanged.
-
-The standard Unix98 identifiers @code{PTHREAD_MUTEX_DEFAULT},
-@code{PTHREAD_MUTEX_NORMAL}, @code{PTHREAD_MUTEX_RECURSIVE},
-and @code{PTHREAD_MUTEX_ERRORCHECK} are also permitted.
-
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_gettype (const pthread_mutexattr_t *@var{attr}, int *@var{type})
-@code{pthread_mutexattr_gettype} retrieves the current value of the
-mutex type attribute in @var{attr} and stores it in the location pointed
-to by @var{type}.
-
-This function always returns 0.
-@end deftypefun
-
-@node Condition Variables
-@section Condition Variables
-
-A condition (short for ``condition variable'') is a synchronization
-device that allows threads to suspend execution until some predicate on
-shared data is satisfied. The basic operations on conditions are: signal
-the condition (when the predicate becomes true), and wait for the
-condition, suspending the thread execution until another thread signals
-the condition.
-
-A condition variable must always be associated with a mutex, to avoid
-the race condition where a thread prepares to wait on a condition
-variable and another thread signals the condition just before the first
-thread actually waits on it.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_init (pthread_cond_t *@var{cond}, pthread_condattr_t *cond_@var{attr})
-
-@code{pthread_cond_init} initializes the condition variable @var{cond},
-using the condition attributes specified in @var{cond_attr}, or default
-attributes if @var{cond_attr} is @code{NULL}. The LinuxThreads
-implementation supports no attributes for conditions, hence the
-@var{cond_attr} parameter is actually ignored.
-
-Variables of type @code{pthread_cond_t} can also be initialized
-statically, using the constant @code{PTHREAD_COND_INITIALIZER}.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_signal (pthread_cond_t *@var{cond})
-@code{pthread_cond_signal} restarts one of the threads that are waiting
-on the condition variable @var{cond}. If no threads are waiting on
-@var{cond}, nothing happens. If several threads are waiting on
-@var{cond}, exactly one is restarted, but it is not specified which.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_broadcast (pthread_cond_t *@var{cond})
-@code{pthread_cond_broadcast} restarts all the threads that are waiting
-on the condition variable @var{cond}. Nothing happens if no threads are
-waiting on @var{cond}.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_wait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex})
-@code{pthread_cond_wait} atomically unlocks the @var{mutex} (as per
-@code{pthread_unlock_mutex}) and waits for the condition variable
-@var{cond} to be signaled. The thread execution is suspended and does
-not consume any CPU time until the condition variable is signaled. The
-@var{mutex} must be locked by the calling thread on entrance to
-@code{pthread_cond_wait}. Before returning to the calling thread,
-@code{pthread_cond_wait} re-acquires @var{mutex} (as per
-@code{pthread_lock_mutex}).
-
-Unlocking the mutex and suspending on the condition variable is done
-atomically. Thus, if all threads always acquire the mutex before
-signaling the condition, this guarantees that the condition cannot be
-signaled (and thus ignored) between the time a thread locks the mutex
-and the time it waits on the condition variable.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_timedwait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex}, const struct timespec *@var{abstime})
-@code{pthread_cond_timedwait} atomically unlocks @var{mutex} and waits
-on @var{cond}, as @code{pthread_cond_wait} does, but it also bounds the
-duration of the wait. If @var{cond} has not been signaled before time
-@var{abstime}, the mutex @var{mutex} is re-acquired and
-@code{pthread_cond_timedwait} returns the error code @code{ETIMEDOUT}.
-The wait can also be interrupted by a signal; in that case
-@code{pthread_cond_timedwait} returns @code{EINTR}.
-
-The @var{abstime} parameter specifies an absolute time, with the same
-origin as @code{time} and @code{gettimeofday}: an @var{abstime} of 0
-corresponds to 00:00:00 GMT, January 1, 1970.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_destroy (pthread_cond_t *@var{cond})
-@code{pthread_cond_destroy} destroys the condition variable @var{cond},
-freeing the resources it might hold. If any threads are waiting on the
-condition variable, @code{pthread_cond_destroy} leaves @var{cond}
-untouched and returns @code{EBUSY}. Otherwise it returns 0, and
-@var{cond} must not be used again until it is reinitialized.
-
-In the LinuxThreads implementation, no resources are associated with
-condition variables, so @code{pthread_cond_destroy} actually does
-nothing.
-@end deftypefun
-
-@code{pthread_cond_wait} and @code{pthread_cond_timedwait} are
-cancellation points. If a thread is canceled while suspended in one of
-these functions, the thread immediately resumes execution, relocks the
-mutex specified by @var{mutex}, and finally executes the cancellation.
-Consequently, cleanup handlers are assured that @var{mutex} is locked
-when they are called.
-
-It is not safe to call the condition variable functions from a signal
-handler. In particular, calling @code{pthread_cond_signal} or
-@code{pthread_cond_broadcast} from a signal handler may deadlock the
-calling thread.
-
-Consider two shared variables @var{x} and @var{y}, protected by the
-mutex @var{mut}, and a condition variable @var{cond} that is to be
-signaled whenever @var{x} becomes greater than @var{y}.
-
-@smallexample
-int x,y;
-pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
-pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
-@end smallexample
-
-Waiting until @var{x} is greater than @var{y} is performed as follows:
-
-@smallexample
-pthread_mutex_lock(&mut);
-while (x <= y) @{
- pthread_cond_wait(&cond, &mut);
-@}
-/* operate on x and y */
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Modifications on @var{x} and @var{y} that may cause @var{x} to become greater than
-@var{y} should signal the condition if needed:
-
-@smallexample
-pthread_mutex_lock(&mut);
-/* modify x and y */
-if (x > y) pthread_cond_broadcast(&cond);
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-If it can be proved that at most one waiting thread needs to be waken
-up (for instance, if there are only two threads communicating through
-@var{x} and @var{y}), @code{pthread_cond_signal} can be used as a slightly more
-efficient alternative to @code{pthread_cond_broadcast}. In doubt, use
-@code{pthread_cond_broadcast}.
-
-To wait for @var{x} to becomes greater than @var{y} with a timeout of 5
-seconds, do:
-
-@smallexample
-struct timeval now;
-struct timespec timeout;
-int retcode;
-
-pthread_mutex_lock(&mut);
-gettimeofday(&now);
-timeout.tv_sec = now.tv_sec + 5;
-timeout.tv_nsec = now.tv_usec * 1000;
-retcode = 0;
-while (x <= y && retcode != ETIMEDOUT) @{
- retcode = pthread_cond_timedwait(&cond, &mut, &timeout);
-@}
-if (retcode == ETIMEDOUT) @{
- /* timeout occurred */
-@} else @{
- /* operate on x and y */
-@}
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Condition attributes can be specified at condition creation time, by
-passing a condition attribute object as second argument to
-@code{pthread_cond_init}. Passing @code{NULL} is equivalent to passing
-a condition attribute object with all attributes set to their default
-values.
-
-The LinuxThreads implementation supports no attributes for
-conditions. The functions on condition attributes are included only for
-compliance with the POSIX standard.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_condattr_init (pthread_condattr_t *@var{attr})
-@deftypefunx int pthread_condattr_destroy (pthread_condattr_t *@var{attr})
-@code{pthread_condattr_init} initializes the condition attribute object
-@var{attr} and fills it with default values for the attributes.
-@code{pthread_condattr_destroy} destroys the condition attribute object
-@var{attr}.
-
-Both functions do nothing in the LinuxThreads implementation.
-
-@code{pthread_condattr_init} and @code{pthread_condattr_destroy} always
-return 0.
-@end deftypefun
-
-@node POSIX Semaphores
-@section POSIX Semaphores
-
-@vindex SEM_VALUE_MAX
-Semaphores are counters for resources shared between threads. The
-basic operations on semaphores are: increment the counter atomically,
-and wait until the counter is non-null and decrement it atomically.
-
-Semaphores have a maximum value past which they cannot be incremented.
-The macro @code{SEM_VALUE_MAX} is defined to be this maximum value. In
-the GNU C library, @code{SEM_VALUE_MAX} is equal to @code{INT_MAX}
-(@pxref{Range of Type}), but it may be much smaller on other systems.
-
-The pthreads library implements POSIX 1003.1b semaphores. These should
-not be confused with System V semaphores (@code{ipc}, @code{semctl} and
-@code{semop}).
-@c !!! SysV IPC is not doc'd at all in our manual
-
-All the semaphore functions and macros are defined in @file{semaphore.h}.
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_init (sem_t *@var{sem}, int @var{pshared}, unsigned int @var{value})
-@code{sem_init} initializes the semaphore object pointed to by
-@var{sem}. The count associated with the semaphore is set initially to
-@var{value}. The @var{pshared} argument indicates whether the semaphore
-is local to the current process (@var{pshared} is zero) or is to be
-shared between several processes (@var{pshared} is not zero).
-
-On success @code{sem_init} returns 0. On failure it returns -1 and sets
-@var{errno} to one of the following values:
-
-@table @code
-@item EINVAL
-@var{value} exceeds the maximal counter value @code{SEM_VALUE_MAX}
-
-@item ENOSYS
-@var{pshared} is not zero. LinuxThreads currently does not support
-process-shared semaphores. (This will eventually change.)
-@end table
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_destroy (sem_t * @var{sem})
-@code{sem_destroy} destroys a semaphore object, freeing the resources it
-might hold. If any threads are waiting on the semaphore when
-@code{sem_destroy} is called, it fails and sets @var{errno} to
-@code{EBUSY}.
-
-In the LinuxThreads implementation, no resources are associated with
-semaphore objects, thus @code{sem_destroy} actually does nothing except
-checking that no thread is waiting on the semaphore. This will change
-when process-shared semaphores are implemented.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_wait (sem_t * @var{sem})
-@code{sem_wait} suspends the calling thread until the semaphore pointed
-to by @var{sem} has non-zero count. It then atomically decreases the
-semaphore count.
-
-@code{sem_wait} is a cancellation point. It always returns 0.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_trywait (sem_t * @var{sem})
-@code{sem_trywait} is a non-blocking variant of @code{sem_wait}. If the
-semaphore pointed to by @var{sem} has non-zero count, the count is
-atomically decreased and @code{sem_trywait} immediately returns 0. If
-the semaphore count is zero, @code{sem_trywait} immediately returns -1
-and sets errno to @code{EAGAIN}.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_post (sem_t * @var{sem})
-@code{sem_post} atomically increases the count of the semaphore pointed to
-by @var{sem}. This function never blocks.
-
-@c !!! This para appears not to agree with the code.
-On processors supporting atomic compare-and-swap (Intel 486, Pentium and
-later, Alpha, PowerPC, MIPS II, Motorola 68k, Ultrasparc), the
-@code{sem_post} function is can safely be called from signal handlers.
-This is the only thread synchronization function provided by POSIX
-threads that is async-signal safe. On the Intel 386 and earlier Sparc
-chips, the current LinuxThreads implementation of @code{sem_post} is not
-async-signal safe, because the hardware does not support the required
-atomic operations.
-
-@code{sem_post} always succeeds and returns 0, unless the semaphore
-count would exceed @code{SEM_VALUE_MAX} after being incremented. In
-that case @code{sem_post} returns -1 and sets @var{errno} to
-@code{EINVAL}. The semaphore count is left unchanged.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_getvalue (sem_t * @var{sem}, int * @var{sval})
-@code{sem_getvalue} stores in the location pointed to by @var{sval} the
-current count of the semaphore @var{sem}. It always returns 0.
-@end deftypefun
-
-@node Thread-Specific Data
-@section Thread-Specific Data
-
-Programs often need global or static variables that have different
-values in different threads. Since threads share one memory space, this
-cannot be achieved with regular variables. Thread-specific data is the
-POSIX threads answer to this need.
-
-Each thread possesses a private memory block, the thread-specific data
-area, or TSD area for short. This area is indexed by TSD keys. The TSD
-area associates values of type @code{void *} to TSD keys. TSD keys are
-common to all threads, but the value associated with a given TSD key can
-be different in each thread.
-
-For concreteness, the TSD areas can be viewed as arrays of @code{void *}
-pointers, TSD keys as integer indices into these arrays, and the value
-of a TSD key as the value of the corresponding array element in the
-calling thread.
-
-When a thread is created, its TSD area initially associates @code{NULL}
-with all keys.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_key_create (pthread_key_t *@var{key}, void (*destr_function) (void *))
-@code{pthread_key_create} allocates a new TSD key. The key is stored in
-the location pointed to by @var{key}. There is a limit of
-@code{PTHREAD_KEYS_MAX} on the number of keys allocated at a given
-time. The value initially associated with the returned key is
-@code{NULL} in all currently executing threads.
-
-The @var{destr_function} argument, if not @code{NULL}, specifies a
-destructor function associated with the key. When a thread terminates
-via @code{pthread_exit} or by cancellation, @var{destr_function} is
-called on the value associated with the key in that thread. The
-@var{destr_function} is not called if a key is deleted with
-@code{pthread_key_delete} or a value is changed with
-@code{pthread_setspecific}. The order in which destructor functions are
-called at thread termination time is unspecified.
-
-Before the destructor function is called, the @code{NULL} value is
-associated with the key in the current thread. A destructor function
-might, however, re-associate non-@code{NULL} values to that key or some
-other key. To deal with this, if after all the destructors have been
-called for all non-@code{NULL} values, there are still some
-non-@code{NULL} values with associated destructors, then the process is
-repeated. The LinuxThreads implementation stops the process after
-@code{PTHREAD_DESTRUCTOR_ITERATIONS} iterations, even if some
-non-@code{NULL} values with associated descriptors remain. Other
-implementations may loop indefinitely.
-
-@code{pthread_key_create} returns 0 unless @code{PTHREAD_KEYS_MAX} keys
-have already been allocated, in which case it fails and returns
-@code{EAGAIN}.
-@end deftypefun
-
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_key_delete (pthread_key_t @var{key})
-@code{pthread_key_delete} deallocates a TSD key. It does not check
-whether non-@code{NULL} values are associated with that key in the
-currently executing threads, nor call the destructor function associated
-with the key.
-
-If there is no such key @var{key}, it returns @code{EINVAL}. Otherwise
-it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setspecific (pthread_key_t @var{key}, const void *@var{pointer})
-@code{pthread_setspecific} changes the value associated with @var{key}
-in the calling thread, storing the given @var{pointer} instead.
-
-If there is no such key @var{key}, it returns @code{EINVAL}. Otherwise
-it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun {void *} pthread_getspecific (pthread_key_t @var{key})
-@code{pthread_getspecific} returns the value currently associated with
-@var{key} in the calling thread.
-
-If there is no such key @var{key}, it returns @code{NULL}.
-@end deftypefun
-
-The following code fragment allocates a thread-specific array of 100
-characters, with automatic reclaimation at thread exit:
-
-@smallexample
-/* Key for the thread-specific buffer */
-static pthread_key_t buffer_key;
-
-/* Once-only initialisation of the key */
-static pthread_once_t buffer_key_once = PTHREAD_ONCE_INIT;
-
-/* Allocate the thread-specific buffer */
-void buffer_alloc(void)
-@{
- pthread_once(&buffer_key_once, buffer_key_alloc);
- pthread_setspecific(buffer_key, malloc(100));
-@}
-
-/* Return the thread-specific buffer */
-char * get_buffer(void)
-@{
- return (char *) pthread_getspecific(buffer_key);
-@}
-
-/* Allocate the key */
-static void buffer_key_alloc()
-@{
- pthread_key_create(&buffer_key, buffer_destroy);
-@}
-
-/* Free the thread-specific buffer */
-static void buffer_destroy(void * buf)
-@{
- free(buf);
-@}
-@end smallexample
-
-@node Threads and Signal Handling
-@section Threads and Signal Handling
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_sigmask (int @var{how}, const sigset_t *@var{newmask}, sigset_t *@var{oldmask})
-@code{pthread_sigmask} changes the signal mask for the calling thread as
-described by the @var{how} and @var{newmask} arguments. If @var{oldmask}
-is not @code{NULL}, the previous signal mask is stored in the location
-pointed to by @var{oldmask}.
-
-The meaning of the @var{how} and @var{newmask} arguments is the same as
-for @code{sigprocmask}. If @var{how} is @code{SIG_SETMASK}, the signal
-mask is set to @var{newmask}. If @var{how} is @code{SIG_BLOCK}, the
-signals specified to @var{newmask} are added to the current signal mask.
-If @var{how} is @code{SIG_UNBLOCK}, the signals specified to
-@var{newmask} are removed from the current signal mask.
-
-Recall that signal masks are set on a per-thread basis, but signal
-actions and signal handlers, as set with @code{sigaction}, are shared
-between all threads.
-
-The @code{pthread_sigmask} function returns 0 on success, and one of the
-following error codes on error:
-@table @code
-@item EINVAL
-@var{how} is not one of @code{SIG_SETMASK}, @code{SIG_BLOCK}, or @code{SIG_UNBLOCK}
-
-@item EFAULT
-@var{newmask} or @var{oldmask} point to invalid addresses
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_kill (pthread_t @var{thread}, int @var{signo})
-@code{pthread_kill} sends signal number @var{signo} to the thread
-@var{thread}. The signal is delivered and handled as described in
-@ref{Signal Handling}.
-
-@code{pthread_kill} returns 0 on success, one of the following error codes
-on error:
-@table @code
-@item EINVAL
-@var{signo} is not a valid signal number
-
-@item ESRCH
-The thread @var{thread} does not exist (e.g. it has already terminated)
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int sigwait (const sigset_t *@var{set}, int *@var{sig})
-@code{sigwait} suspends the calling thread until one of the signals in
-@var{set} is delivered to the calling thread. It then stores the number
-of the signal received in the location pointed to by @var{sig} and
-returns. The signals in @var{set} must be blocked and not ignored on
-entrance to @code{sigwait}. If the delivered signal has a signal handler
-function attached, that function is @emph{not} called.
-
-@code{sigwait} is a cancellation point. It always returns 0.
-@end deftypefun
-
-For @code{sigwait} to work reliably, the signals being waited for must be
-blocked in all threads, not only in the calling thread, since
-otherwise the POSIX semantics for signal delivery do not guarantee
-that it's the thread doing the @code{sigwait} that will receive the signal.
-The best way to achieve this is block those signals before any threads
-are created, and never unblock them in the program other than by
-calling @code{sigwait}.
-
-Signal handling in LinuxThreads departs significantly from the POSIX
-standard. According to the standard, ``asynchronous'' (external) signals
-are addressed to the whole process (the collection of all threads),
-which then delivers them to one particular thread. The thread that
-actually receives the signal is any thread that does not currently block
-the signal.
-
-In LinuxThreads, each thread is actually a kernel process with its own
-PID, so external signals are always directed to one particular thread.
-If, for instance, another thread is blocked in @code{sigwait} on that
-signal, it will not be restarted.
-
-The LinuxThreads implementation of @code{sigwait} installs dummy signal
-handlers for the signals in @var{set} for the duration of the
-wait. Since signal handlers are shared between all threads, other
-threads must not attach their own signal handlers to these signals, or
-alternatively they should all block these signals (which is recommended
-anyway).
-
-@node Threads and Fork
-@section Threads and Fork
-
-It's not intuitively obvious what should happen when a multi-threaded POSIX
-process calls @code{fork}. Not only are the semantics tricky, but you may
-need to write code that does the right thing at fork time even if that code
-doesn't use the @code{fork} function. Moreover, you need to be aware of
-interaction between @code{fork} and some library features like
-@code{pthread_once} and stdio streams.
-
-When @code{fork} is called by one of the threads of a process, it creates a new
-process which is copy of the calling process. Effectively, in addition to
-copying certain system objects, the function takes a snapshot of the memory
-areas of the parent process, and creates identical areas in the child.
-To make matters more complicated, with threads it's possible for two or more
-threads to concurrently call fork to create two or more child processes.
-
-The child process has a copy of the address space of the parent, but it does
-not inherit any of its threads. Execution of the child process is carried out
-by a new thread which returns from @code{fork} function with a return value of
-zero; it is the only thread in the child process. Because threads are not
-inherited across fork, issues arise. At the time of the call to @code{fork},
-threads in the parent process other than the one calling @code{fork} may have
-been executing critical regions of code. As a result, the child process may
-get a copy of objects that are not in a well-defined state. This potential
-problem affects all components of the program.
-
-Any program component which will continue being used in a child process must
-correctly handle its state during @code{fork}. For this purpose, the POSIX
-interface provides the special function @code{pthread_atfork} for installing
-pointers to handler functions which are called from within @code{fork}.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_atfork (void (*@var{prepare})(void), void (*@var{parent})(void), void (*@var{child})(void))
-
-@code{pthread_atfork} registers handler functions to be called just
-before and just after a new process is created with @code{fork}. The
-@var{prepare} handler will be called from the parent process, just
-before the new process is created. The @var{parent} handler will be
-called from the parent process, just before @code{fork} returns. The
-@var{child} handler will be called from the child process, just before
-@code{fork} returns.
-
-@code{pthread_atfork} returns 0 on success and a non-zero error code on
-error.
-
-One or more of the three handlers @var{prepare}, @var{parent} and
-@var{child} can be given as @code{NULL}, meaning that no handler needs
-to be called at the corresponding point.
-
-@code{pthread_atfork} can be called several times to install several
-sets of handlers. At @code{fork} time, the @var{prepare} handlers are
-called in LIFO order (last added with @code{pthread_atfork}, first
-called before @code{fork}), while the @var{parent} and @var{child}
-handlers are called in FIFO order (first added, first called).
-
-If there is insufficient memory available to register the handlers,
-@code{pthread_atfork} fails and returns @code{ENOMEM}. Otherwise it
-returns 0.
-
-The functions @code{fork} and @code{pthread_atfork} must not be regarded as
-reentrant from the context of the handlers. That is to say, if a
-@code{pthread_atfork} handler invoked from within @code{fork} calls
-@code{pthread_atfork} or @code{fork}, the behavior is undefined.
-
-Registering a triplet of handlers is an atomic operation with respect to fork.
-If new handlers are registered at about the same time as a fork occurs, either
-all three handlers will be called, or none of them will be called.
-
-The handlers are inherited by the child process, and there is no
-way to remove them, short of using @code{exec} to load a new
-pocess image.
-
-@end deftypefun
-
-To understand the purpose of @code{pthread_atfork}, recall that
-@code{fork} duplicates the whole memory space, including mutexes in
-their current locking state, but only the calling thread: other threads
-are not running in the child process. The mutexes are not usable after
-the @code{fork} and must be initialized with @code{pthread_mutex_init}
-in the child process. This is a limitation of the current
-implementation and might or might not be present in future versions.
-
-To avoid this, install handlers with @code{pthread_atfork} as follows: have the
-@var{prepare} handler lock the mutexes (in locking order), and the
-@var{parent} handler unlock the mutexes. The @var{child} handler should reset
-the mutexes using @code{pthread_mutex_init}, as well as any other
-synchronization objects such as condition variables.
-
-Locking the global mutexes before the fork ensures that all other threads are
-locked out of the critical regions of code protected by those mutexes. Thus
-when @code{fork} takes a snapshot of the parent's address space, that snapshot
-will copy valid, stable data. Resetting the synchronization objects in the
-child process will ensure they are properly cleansed of any artifacts from the
-threading subsystem of the parent process. For example, a mutex may inherit
-a wait queue of threads waiting for the lock; this wait queue makes no sense
-in the child process. Initializing the mutex takes care of this.
-
-@node Streams and Fork
-@section Streams and Fork
-
-The GNU standard I/O library has an internal mutex which guards the internal
-linked list of all standard C FILE objects. This mutex is properly taken care
-of during @code{fork} so that the child receives an intact copy of the list.
-This allows the @code{fopen} function, and related stream-creating functions,
-to work correctly in the child process, since these functions need to insert
-into the list.
-
-However, the individual stream locks are not completely taken care of. Thus
-unless the multithreaded application takes special precautions in its use of
-@code{fork}, the child process might not be able to safely use the streams that
-it inherited from the parent. In general, for any given open stream in the
-parent that is to be used by the child process, the application must ensure
-that that stream is not in use by another thread when @code{fork} is called.
-Otherwise an inconsistent copy of the stream object be produced. An easy way to
-ensure this is to use @code{flockfile} to lock the stream prior to calling
-@code{fork} and then unlock it with @code{funlockfile} inside the parent
-process, provided that the parent's threads properly honor these locks.
-Nothing special needs to be done in the child process, since the library
-internally resets all stream locks.
-
-Note that the stream locks are not shared between the parent and child.
-For example, even if you ensure that, say, the stream @code{stdout} is properly
-treated and can be safely used in the child, the stream locks do not provide
-an exclusion mechanism between the parent and child. If both processes write
-to @code{stdout}, strangely interleaved output may result regardless of
-the explicit use of @code{flockfile} or implicit locks.
-
-Also note that these provisions are a GNU extension; other systems might not
-provide any way for streams to be used in the child of a multithreaded process.
-POSIX requires that such a child process confines itself to calling only
-asynchronous safe functions, which excludes much of the library, including
-standard I/O.
-
-@node Miscellaneous Thread Functions
-@section Miscellaneous Thread Functions
-
-@comment pthread.h
-@comment POSIX
-@deftypefun {pthread_t} pthread_self (@var{void})
-@code{pthread_self} returns the thread identifier for the calling thread.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_equal (pthread_t thread1, pthread_t thread2)
-@code{pthread_equal} determines if two thread identifiers refer to the same
-thread.
-
-A non-zero value is returned if @var{thread1} and @var{thread2} refer to
-the same thread. Otherwise, 0 is returned.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_detach (pthread_t @var{th})
-@code{pthread_detach} puts the thread @var{th} in the detached
-state. This guarantees that the memory resources consumed by @var{th}
-will be freed immediately when @var{th} terminates. However, this
-prevents other threads from synchronizing on the termination of @var{th}
-using @code{pthread_join}.
-
-A thread can be created initially in the detached state, using the
-@code{detachstate} attribute to @code{pthread_create}. In contrast,
-@code{pthread_detach} applies to threads created in the joinable state,
-and which need to be put in the detached state later.
-
-After @code{pthread_detach} completes, subsequent attempts to perform
-@code{pthread_join} on @var{th} will fail. If another thread is already
-joining the thread @var{th} at the time @code{pthread_detach} is called,
-@code{pthread_detach} does nothing and leaves @var{th} in the joinable
-state.
-
-On success, 0 is returned. On error, one of the following codes is
-returned:
-@table @code
-@item ESRCH
-No thread could be found corresponding to that specified by @var{th}
-@item EINVAL
-The thread @var{th} is already in the detached state
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_kill_other_threads_np (@var{void})
-@code{pthread_kill_other_threads_np} is a non-portable LinuxThreads extension.
-It causes all threads in the program to terminate immediately, except
-the calling thread which proceeds normally. It is intended to be
-called just before a thread calls one of the @code{exec} functions,
-e.g. @code{execve}.
-
-Termination of the other threads is not performed through
-@code{pthread_cancel} and completely bypasses the cancellation
-mechanism. Hence, the current settings for cancellation state and
-cancellation type are ignored, and the cleanup handlers are not
-executed in the terminated threads.
-
-According to POSIX 1003.1c, a successful @code{exec*} in one of the
-threads should automatically terminate all other threads in the program.
-This behavior is not yet implemented in LinuxThreads. Calling
-@code{pthread_kill_other_threads_np} before @code{exec*} achieves much
-of the same behavior, except that if @code{exec*} ultimately fails, then
-all other threads are already killed.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_once (pthread_once_t *once_@var{control}, void (*@var{init_routine}) (void))
-
-The purpose of @code{pthread_once} is to ensure that a piece of
-initialization code is executed at most once. The @var{once_control}
-argument points to a static or extern variable statically initialized
-to @code{PTHREAD_ONCE_INIT}.
-
-The first time @code{pthread_once} is called with a given
-@var{once_control} argument, it calls @var{init_routine} with no
-argument and changes the value of the @var{once_control} variable to
-record that initialization has been performed. Subsequent calls to
-@code{pthread_once} with the same @code{once_control} argument do
-nothing.
-
-If a thread is cancelled while executing @var{init_routine}
-the state of the @var{once_control} variable is reset so that
-a future call to @code{pthread_once} will call the routine again.
-
-If the process forks while one or more threads are executing
-@code{pthread_once} initialization routines, the states of their respective
-@var{once_control} variables will appear to be reset in the child process so
-that if the child calls @code{pthread_once}, the routines will be executed.
-
-@code{pthread_once} always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setschedparam (pthread_t target_@var{thread}, int @var{policy}, const struct sched_param *@var{param})
-
-@code{pthread_setschedparam} sets the scheduling parameters for the
-thread @var{target_thread} as indicated by @var{policy} and
-@var{param}. @var{policy} can be either @code{SCHED_OTHER} (regular,
-non-realtime scheduling), @code{SCHED_RR} (realtime, round-robin) or
-@code{SCHED_FIFO} (realtime, first-in first-out). @var{param} specifies
-the scheduling priority for the two realtime policies. See
-@code{sched_setpolicy} for more information on scheduling policies.
-
-The realtime scheduling policies @code{SCHED_RR} and @code{SCHED_FIFO}
-are available only to processes with superuser privileges.
-
-On success, @code{pthread_setschedparam} returns 0. On error it returns
-one of the following codes:
-@table @code
-@item EINVAL
-@var{policy} is not one of @code{SCHED_OTHER}, @code{SCHED_RR},
-@code{SCHED_FIFO}, or the priority value specified by @var{param} is not
-valid for the specified policy
-
-@item EPERM
-Realtime scheduling was requested but the calling process does not have
-sufficient privileges.
-
-@item ESRCH
-The @var{target_thread} is invalid or has already terminated
-
-@item EFAULT
-@var{param} points outside the process memory space
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_getschedparam (pthread_t target_@var{thread}, int *@var{policy}, struct sched_param *@var{param})
-
-@code{pthread_getschedparam} retrieves the scheduling policy and
-scheduling parameters for the thread @var{target_thread} and stores them
-in the locations pointed to by @var{policy} and @var{param},
-respectively.
-
-@code{pthread_getschedparam} returns 0 on success, or one of the
-following error codes on failure:
-@table @code
-@item ESRCH
-The @var{target_thread} is invalid or has already terminated.
-
-@item EFAULT
-@var{policy} or @var{param} point outside the process memory space.
-
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setconcurrency (int @var{level})
-@code{pthread_setconcurrency} is unused in LinuxThreads due to the lack
-of a mapping of user threads to kernel threads. It exists for source
-compatibility. It does store the value @var{level} so that it can be
-returned by a subsequent call to @code{pthread_getconcurrency}. It takes
-no other action however.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_getconcurrency ()
-@code{pthread_getconcurrency} is unused in LinuxThreads due to the lack
-of a mapping of user threads to kernel threads. It exists for source
-compatibility. However, it will return the value that was set by the
-last call to @code{pthread_setconcurrency}.
-@end deftypefun
Modified: glibc-doc-reference/tags/2.13-1/manual/locale.texi
===================================================================
--- glibc-doc-reference/trunk/manual/locale.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/locale.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1210,7 +1210,7 @@
/* @r{Prepare the @code{getline} call.} */
line = NULL;
len = 0;
- while (getline (&line, &len, stdout) >= 0)
+ while (getline (&line, &len, stdin) >= 0)
@{
/* @r{Check the response.} */
int res = rpmatch (line);
Modified: glibc-doc-reference/tags/2.13-1/manual/math.texi
===================================================================
--- glibc-doc-reference/trunk/manual/math.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/math.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1421,7 +1421,7 @@
The GNU C library contains four additional functions which contain the
state as an explicit parameter and therefore make it possible to handle
-thread-local PRNGs. Beside this there are no difference. In fact, the
+thread-local PRNGs. Beside this there is no difference. In fact, the
four functions already discussed are implemented internally using the
following interfaces.
Modified: glibc-doc-reference/tags/2.13-1/manual/memory.texi
===================================================================
--- glibc-doc-reference/trunk/manual/memory.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/memory.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -702,6 +702,11 @@
@item M_MMAP_MAX
The maximum number of chunks to allocate with @code{mmap}. Setting this
to zero disables all use of @code{mmap}.
+@item M_PERTURB
+If non-zero, memory blocks are filled with values depending on some
+low order bits of this parameter when they are allocated (except when
+allocated by @code{calloc}) and freed. This can be used to debug the
+use of uninitialized or freed heap memory.
@end table
@end deftypefun
@@ -2379,7 +2384,7 @@
@c The Brk system call in Linux (as opposed to the GNU C Library function)
@c is considerably different. It always returns the new end of the data
@c segment, whether it succeeds or fails. The GNU C library Brk determines
-@c it's a failure if and only if if the system call returns an address less
+@c it's a failure if and only if the system call returns an address less
@c than the address requested.
@end deftypefun
Modified: glibc-doc-reference/tags/2.13-1/manual/message.texi
===================================================================
--- glibc-doc-reference/trunk/manual/message.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/message.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1466,7 +1466,7 @@
handle these kind of problems with the @code{gettext} functions.
@noindent
-As as example consider the following fictional situation. A GUI program
+As an example consider the following fictional situation. A GUI program
has a menu bar with the following entries:
@smallexample
Copied: glibc-doc-reference/tags/2.13-1/manual/pkgvers.texi (from rev 4338, glibc-doc-reference/trunk/manual/pkgvers.texi)
===================================================================
--- glibc-doc-reference/tags/2.13-1/manual/pkgvers.texi (rev 0)
+++ glibc-doc-reference/tags/2.13-1/manual/pkgvers.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,2 @@
+@set PKGVERSION
+@set REPORT_BUGS_TO
Modified: glibc-doc-reference/tags/2.13-1/manual/resource.texi
===================================================================
--- glibc-doc-reference/trunk/manual/resource.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/resource.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1288,7 +1288,7 @@
The POSIX standard up to this date is of not much help to solve this
problem. The Linux kernel provides a set of interfaces to allow
specifying @emph{affinity sets} for a process. The scheduler will
-schedule the thread or process on on CPUs specified by the affinity
+schedule the thread or process on CPUs specified by the affinity
masks. The interfaces which the GNU C library define follow to some
extend the Linux kernel interface.
Modified: glibc-doc-reference/tags/2.13-1/manual/stdio.texi
===================================================================
--- glibc-doc-reference/trunk/manual/stdio.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/stdio.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -574,7 +574,7 @@
introduction of threads) were implemented as macros which are very fast
if the buffer is not empty. With the addition of locking requirements
these functions are no longer implemented as macros since they would
-would expand to too much code.
+expand to too much code.
But these macros are still available with the same functionality under the new
names @code{putc_unlocked} and @code{getc_unlocked}. This possibly huge
difference of speed also suggests the use of the @code{_unlocked}
Added: glibc-doc-reference/tags/2.13-1/manual/texis
===================================================================
--- glibc-doc-reference/tags/2.13-1/manual/texis (rev 0)
+++ glibc-doc-reference/tags/2.13-1/manual/texis 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,89 @@
+texis = \
+intro.texi \
+creature.texi \
+errno.texi \
+memory.texi \
+ctype.texi \
+string.texi \
+stpcpy.c.texi \
+strdupa.c.texi \
+strncat.c.texi \
+charset.texi \
+locale.texi \
+message.texi \
+search.texi \
+search.c.texi \
+pattern.texi \
+io.texi \
+stdio.texi \
+rprintf.c.texi \
+memopen.c.texi \
+memstrm.c.texi \
+fmtmsgexpl.c.texi \
+llio.texi \
+select.c.texi \
+filesys.texi \
+dir.c.texi \
+dir2.c.texi \
+pipe.texi \
+pipe.c.texi \
+popen.c.texi \
+socket.texi \
+mkfsock.c.texi \
+mkisock.c.texi \
+isockad.c.texi \
+inetcli.c.texi \
+inetsrv.c.texi \
+filesrv.c.texi \
+filecli.c.texi \
+terminal.texi \
+termios.c.texi \
+syslog.texi \
+math.texi \
+libm-err.texi \
+arith.texi \
+time.texi \
+strftim.c.texi \
+resource.texi \
+setjmp.texi \
+setjmp.c.texi \
+swapcontext.c.texi \
+signal.texi \
+sigh1.c.texi \
+sigusr.c.texi \
+startup.texi \
+getopt.texi \
+testopt.c.texi \
+longopt.c.texi \
+argp.texi \
+argp-ex1.c.texi \
+argp-ex2.c.texi \
+argp-ex3.c.texi \
+argp-ex4.c.texi \
+subopt.c.texi \
+atexit.c.texi \
+process.texi \
+job.texi \
+nss.texi \
+nsswitch.texi \
+users.texi \
+db.c.texi \
+sysinfo.texi \
+conf.texi \
+crypt.texi \
+mygetpass.c.texi \
+genpass.c.texi \
+testpass.c.texi \
+debug.texi \
+execinfo.c.texi \
+lang.texi \
+add.c.texi \
+header.texi \
+summary.texi \
+install.texi \
+maint.texi \
+contrib.texi \
+freemanuals.texi \
+lesser.texi \
+fdl.texi \
+
Modified: glibc-doc-reference/tags/2.13-1/manual/time.texi
===================================================================
--- glibc-doc-reference/trunk/manual/time.texi 2009-09-30 22:55:05 UTC (rev 3862)
+++ glibc-doc-reference/tags/2.13-1/manual/time.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -972,7 +972,7 @@
large offsets or jitter).
@item long int stbcnt
-This counter denotes the number of of calibrations where the stability
+This counter denotes the number of calibrations where the stability
exceeded the threshold.
@end table
@end deftp
Deleted: glibc-doc-reference/trunk/manual/.cvsignore
===================================================================
--- glibc-doc-reference/trunk/manual/.cvsignore 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/.cvsignore 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,14 +0,0 @@
-*.d *.o *.so *.po *.go stamp.* *.stamp *.ustamp *.udeps
-*.gz *.Z *.tar *.tgz *.bz2
-=*
-TODO COPYING* AUTHORS copyr-* copying.*
-glibc-*
-
-*.dvi* *.info* *.c.texi *.ps *.pdf
-*.toc *.aux *.log *.tmp
-*.cp *.cps *.fn *.fns *.vr *.vrs *.tp *.tps *.ky *.kys *.pg *.pgs
-
-texis top-menu.texi chapters.texi summary.texi stamp-*
-distinfo dir-add.texinfo dir-add.texi
-
-libm-err.texi
Added: glibc-doc-reference/trunk/manual/.gitignore
===================================================================
--- glibc-doc-reference/trunk/manual/.gitignore (rev 0)
+++ glibc-doc-reference/trunk/manual/.gitignore 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,29 @@
+*.aux
+*.c.texi
+*.cp
+*.cps
+*.dvi*
+*.fn
+*.fns
+*.info*
+*.ky
+*.kys
+*.log
+*.pdf
+*.pg
+*.pgs
+*.ps
+*.tmp
+*.toc
+*.tp
+*.tps
+*.vr
+*.vrs
+chapters.texi
+dir-add.texi
+dir-add.texinfo
+libm-err.texi
+stamp-*
+summary.texi
+texis
+top-menu.texi
Modified: glibc-doc-reference/trunk/manual/Makefile
===================================================================
--- glibc-doc-reference/trunk/manual/Makefile 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/Makefile 2011-05-02 18:20:00 UTC (rev 4639)
@@ -58,7 +58,7 @@
pipe socket terminal syslog math arith time \
resource setjmp signal startup process job nss \
users sysinfo conf crypt debug)
-add-chapters = linuxthreads.texi
+add-chapters = $(wildcard $(foreach d, $(add-ons), ../$d/$d.texi))
appendices = lang.texi header.texi install.texi maint.texi contrib.texi \
freemanuals.texi
@@ -232,9 +232,12 @@
.PHONY: stubs
stubs: $(objpfx)stubs
endif
-$(objpfx)stubs ../po/manual.pot $(objpfx)stamp%:
+$(objpfx)stubs ../po/manual.pot:
$(make-target-directory)
touch $@
+$(objpfx)stamp%:
+ $(make-target-directory)
+ touch $@
# Make the target directory if it doesn't exist, using the `mkinstalldirs'
# script that does `mkdir -p' even if `mkdir' doesn't support that flag.
Modified: glibc-doc-reference/trunk/manual/arith.texi
===================================================================
--- glibc-doc-reference/trunk/manual/arith.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/arith.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1407,7 +1407,8 @@
@comment ISO
@deftypefunx {long double} roundl (long double @var{x})
These functions are similar to @code{rint}, but they round halfway
-cases away from zero instead of to the nearest even integer.
+cases away from zero instead of to the nearest integer (or other
+current rounding mode).
@end deftypefun
@comment math.h
Modified: glibc-doc-reference/trunk/manual/charset.texi
===================================================================
--- glibc-doc-reference/trunk/manual/charset.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/charset.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -393,7 +393,7 @@
by the functions we are about to describe. Each locale uses its own
character set (given as an argument to @code{localedef}) and this is the
one assumed as the external multibyte encoding. The wide character
-character set always is UCS-4, at least on GNU systems.
+set is always UCS-4, at least on GNU systems.
A characteristic of each multibyte character set is the maximum number
of bytes that can be necessary to represent one character. This
@@ -577,8 +577,8 @@
and is declared in @file{wchar.h}.
@end deftypefun
-Despite the limitation that the single byte value always is interpreted
-in the initial state this function is actually useful most of the time.
+Despite the limitation that the single byte value is always interpreted
+in the initial state, this function is actually useful most of the time.
Most characters are either entirely single-byte character sets or they
are extension to ASCII. But then it is possible to write code like this
(not that this specific example is very useful):
@@ -607,10 +607,10 @@
on the character of the character set used for @code{wchar_t}
representation. In other situations the bytes are not constant at
compile time and so the compiler cannot do the work. In situations like
-this it is necessary @code{btowc}.
+this, using @code{btowc} is required.
@noindent
-There also is a function for the conversion in the other direction.
+There is also a function for the conversion in the other direction.
@comment wchar.h
@comment ISO
Modified: glibc-doc-reference/trunk/manual/errno.texi
===================================================================
--- glibc-doc-reference/trunk/manual/errno.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/errno.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1265,6 +1265,12 @@
@comment errno ???/???
@end deftypevr
+@comment errno.h
+@comment Linux: Operation not possible due to RF-kill
+@deftypevr Macro int ERFKILL
+@comment errno ???/???
+@end deftypevr
+
@node Error Messages, , Error Codes, Error Reporting
@section Error Messages
@@ -1419,7 +1425,7 @@
@code{perror} generates is not what is wanted and there is no way to
extend or change what @code{perror} does. The GNU coding standard, for
instance, requires error messages to be preceded by the program name and
-programs which read some input files should should provide information
+programs which read some input files should provide information
about the input file name and the line number in case an error is
encountered while reading the file. For these occasions there are two
functions available which are widely used throughout the GNU project.
Modified: glibc-doc-reference/trunk/manual/getopt.texi
===================================================================
--- glibc-doc-reference/trunk/manual/getopt.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/getopt.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -269,7 +269,7 @@
@var{argv} of the next remaining argument.
@end deftypefun
-Since long option names were used before before the @code{getopt_long}
+Since long option names were used before the @code{getopt_long}
options was invented there are program interfaces which require programs
to recognize options like @w{@samp{-option value}} instead of
@w{@samp{--option value}}. To enable these programs to use the GNU
Modified: glibc-doc-reference/trunk/manual/install.texi
===================================================================
--- glibc-doc-reference/trunk/manual/install.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/install.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -330,16 +330,15 @@
@item
GCC 3.4 or newer, GCC 4.1 recommended
-The GNU C library can only be compiled with the GNU C compiler family.
-For the 2.3 releases, GCC 3.2 or higher is required; GCC 3.4 is the
-compiler we advise to use for 2.3 versions.
-For the 2.4 release, GCC 3.4 or higher is required; as of this
-writing, GCC 4.1 is the compiler we advise to use for current versions.
+For the 2.4 release or later, GCC 3.4 or higher is required; as of this
+writing, GCC 4.4 is the compiler we advise to use for current versions.
On certain machines including @code{powerpc64}, compilers prior to GCC
4.0 have bugs that prevent them compiling the C library code in the
2.4 release. On other machines, GCC 4.1 is required to build the C
library with support for the correct @code{long double} type format;
-these include @code{powerpc} (32 bit), @code{s390} and @code{s390x}.
+these include @code{powerpc} (32 bit), @code{s390} and @code{s390x}. For
+other architectures special compiler-provided headers are needed
+(like @file{cpuid.h} on x86) which only come with later compiler versions.
You can use whatever compiler you like to compile programs that use GNU
libc, but be aware that both GCC 2.7 and 2.8 have bugs in their
Modified: glibc-doc-reference/trunk/manual/libc.texinfo
===================================================================
--- glibc-doc-reference/trunk/manual/libc.texinfo 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/libc.texinfo 2011-05-02 18:20:00 UTC (rev 4639)
@@ -29,10 +29,10 @@
of @cite{The GNU C Library Reference Manual}, for version @value{VERSION}.
Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
-2003, 2007, 2008 Free Software Foundation, Inc.
+2003, 2007, 2008, 2010 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.2 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Free Software Needs Free Documentation''
and ``GNU Lesser General Public License'', the Front-Cover texts being
Deleted: glibc-doc-reference/trunk/manual/linuxthreads.texi
===================================================================
--- glibc-doc-reference/trunk/manual/linuxthreads.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/linuxthreads.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1,1627 +0,0 @@
-@node POSIX Threads
-@c @node POSIX Threads, , Top, Top
-@chapter POSIX Threads
-@c %MENU% The standard threads library
-
-@c This chapter needs more work bigtime. -zw
-
-This chapter describes the pthreads (POSIX threads) library. This
-library provides support functions for multithreaded programs: thread
-primitives, synchronization objects, and so forth. It also implements
-POSIX 1003.1b semaphores (not to be confused with System V semaphores).
-
-The threads operations (@samp{pthread_*}) do not use @var{errno}.
-Instead they return an error code directly. The semaphore operations do
-use @var{errno}.
-
-@menu
-* Basic Thread Operations:: Creating, terminating, and waiting for threads.
-* Thread Attributes:: Tuning thread scheduling.
-* Cancellation:: Stopping a thread before it's done.
-* Cleanup Handlers:: Deallocating resources when a thread is
- canceled.
-* Mutexes:: One way to synchronize threads.
-* Condition Variables:: Another way.
-* POSIX Semaphores:: And a third way.
-* Thread-Specific Data:: Variables with different values in
- different threads.
-* Threads and Signal Handling:: Why you should avoid mixing the two, and
- how to do it if you must.
-* Threads and Fork:: Interactions between threads and the
- @code{fork} function.
-* Streams and Fork:: Interactions between stdio streams and
- @code{fork}.
-* Miscellaneous Thread Functions:: A grab bag of utility routines.
-@end menu
-
-@node Basic Thread Operations
-@section Basic Thread Operations
-
-These functions are the thread equivalents of @code{fork}, @code{exit},
-and @code{wait}.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_create (pthread_t * @var{thread}, pthread_attr_t * @var{attr}, void * (*@var{start_routine})(void *), void * @var{arg})
-@code{pthread_create} creates a new thread of control that executes
-concurrently with the calling thread. The new thread calls the
-function @var{start_routine}, passing it @var{arg} as first argument. The
-new thread terminates either explicitly, by calling @code{pthread_exit},
-or implicitly, by returning from the @var{start_routine} function. The
-latter case is equivalent to calling @code{pthread_exit} with the result
-returned by @var{start_routine} as exit code.
-
-The @var{attr} argument specifies thread attributes to be applied to the
-new thread. @xref{Thread Attributes}, for details. The @var{attr}
-argument can also be @code{NULL}, in which case default attributes are
-used: the created thread is joinable (not detached) and has an ordinary
-(not realtime) scheduling policy.
-
-On success, the identifier of the newly created thread is stored in the
-location pointed by the @var{thread} argument, and a 0 is returned. On
-error, a non-zero error code is returned.
-
-This function may return the following errors:
-@table @code
-@item EAGAIN
-Not enough system resources to create a process for the new thread,
-or more than @code{PTHREAD_THREADS_MAX} threads are already active.
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_exit (void *@var{retval})
-@code{pthread_exit} terminates the execution of the calling thread. All
-cleanup handlers (@pxref{Cleanup Handlers}) that have been set for the
-calling thread with @code{pthread_cleanup_push} are executed in reverse
-order (the most recently pushed handler is executed first). Finalization
-functions for thread-specific data are then called for all keys that
-have non-@code{NULL} values associated with them in the calling thread
-(@pxref{Thread-Specific Data}). Finally, execution of the calling
-thread is stopped.
-
-The @var{retval} argument is the return value of the thread. It can be
-retrieved from another thread using @code{pthread_join}.
-
-The @code{pthread_exit} function never returns.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cancel (pthread_t @var{thread})
-
-@code{pthread_cancel} sends a cancellation request to the thread denoted
-by the @var{thread} argument. If there is no such thread,
-@code{pthread_cancel} fails and returns @code{ESRCH}. Otherwise it
-returns 0. @xref{Cancellation}, for details.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_join (pthread_t @var{th}, void **thread_@var{return})
-@code{pthread_join} suspends the execution of the calling thread until
-the thread identified by @var{th} terminates, either by calling
-@code{pthread_exit} or by being canceled.
-
-If @var{thread_return} is not @code{NULL}, the return value of @var{th}
-is stored in the location pointed to by @var{thread_return}. The return
-value of @var{th} is either the argument it gave to @code{pthread_exit},
-or @code{PTHREAD_CANCELED} if @var{th} was canceled.
-
-The joined thread @code{th} must be in the joinable state: it must not
-have been detached using @code{pthread_detach} or the
-@code{PTHREAD_CREATE_DETACHED} attribute to @code{pthread_create}.
-
-When a joinable thread terminates, its memory resources (thread
-descriptor and stack) are not deallocated until another thread performs
-@code{pthread_join} on it. Therefore, @code{pthread_join} must be called
-once for each joinable thread created to avoid memory leaks.
-
-At most one thread can wait for the termination of a given
-thread. Calling @code{pthread_join} on a thread @var{th} on which
-another thread is already waiting for termination returns an error.
-
-@code{pthread_join} is a cancellation point. If a thread is canceled
-while suspended in @code{pthread_join}, the thread execution resumes
-immediately and the cancellation is executed without waiting for the
-@var{th} thread to terminate. If cancellation occurs during
-@code{pthread_join}, the @var{th} thread remains not joined.
-
-On success, the return value of @var{th} is stored in the location
-pointed to by @var{thread_return}, and 0 is returned. On error, one of
-the following values is returned:
-@table @code
-@item ESRCH
-No thread could be found corresponding to that specified by @var{th}.
-@item EINVAL
-The @var{th} thread has been detached, or another thread is already
-waiting on termination of @var{th}.
-@item EDEADLK
-The @var{th} argument refers to the calling thread.
-@end table
-@end deftypefun
-
-@node Thread Attributes
-@section Thread Attributes
-
-@comment pthread.h
-@comment POSIX
-
-Threads have a number of attributes that may be set at creation time.
-This is done by filling a thread attribute object @var{attr} of type
-@code{pthread_attr_t}, then passing it as second argument to
-@code{pthread_create}. Passing @code{NULL} is equivalent to passing a
-thread attribute object with all attributes set to their default values.
-
-Attribute objects are consulted only when creating a new thread. The
-same attribute object can be used for creating several threads.
-Modifying an attribute object after a call to @code{pthread_create} does
-not change the attributes of the thread previously created.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_init (pthread_attr_t *@var{attr})
-@code{pthread_attr_init} initializes the thread attribute object
-@var{attr} and fills it with default values for the attributes. (The
-default values are listed below for each attribute.)
-
-Each attribute @var{attrname} (see below for a list of all attributes)
-can be individually set using the function
-@code{pthread_attr_set@var{attrname}} and retrieved using the function
-@code{pthread_attr_get@var{attrname}}.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_destroy (pthread_attr_t *@var{attr})
-@code{pthread_attr_destroy} destroys the attribute object pointed to by
-@var{attr} releasing any resources associated with it. @var{attr} is
-left in an undefined state, and you must not use it again in a call to
-any pthreads function until it has been reinitialized.
-@end deftypefun
-
-@findex pthread_attr_setdetachstate
-@findex pthread_attr_setguardsize
-@findex pthread_attr_setinheritsched
-@findex pthread_attr_setschedparam
-@findex pthread_attr_setschedpolicy
-@findex pthread_attr_setscope
-@findex pthread_attr_setstack
-@findex pthread_attr_setstackaddr
-@findex pthread_attr_setstacksize
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_setattr (pthread_attr_t *@var{obj}, int @var{value})
-Set attribute @var{attr} to @var{value} in the attribute object pointed
-to by @var{obj}. See below for a list of possible attributes and the
-values they can take.
-
-On success, these functions return 0. If @var{value} is not meaningful
-for the @var{attr} being modified, they will return the error code
-@code{EINVAL}. Some of the functions have other failure modes; see
-below.
-@end deftypefun
-
-@findex pthread_attr_getdetachstate
-@findex pthread_attr_getguardsize
-@findex pthread_attr_getinheritsched
-@findex pthread_attr_getschedparam
-@findex pthread_attr_getschedpolicy
-@findex pthread_attr_getscope
-@findex pthread_attr_getstack
-@findex pthread_attr_getstackaddr
-@findex pthread_attr_getstacksize
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_attr_getattr (const pthread_attr_t *@var{obj}, int *@var{value})
-Store the current setting of @var{attr} in @var{obj} into the variable
-pointed to by @var{value}.
-
-These functions always return 0.
-@end deftypefun
-
-The following thread attributes are supported:
-@table @samp
-@item detachstate
-Choose whether the thread is created in the joinable state (value
-@code{PTHREAD_CREATE_JOINABLE}) or in the detached state
-(@code{PTHREAD_CREATE_DETACHED}). The default is
-@code{PTHREAD_CREATE_JOINABLE}.
-
-In the joinable state, another thread can synchronize on the thread
-termination and recover its termination code using @code{pthread_join},
-but some of the thread resources are kept allocated after the thread
-terminates, and reclaimed only when another thread performs
-@code{pthread_join} on that thread.
-
-In the detached state, the thread resources are immediately freed when
-it terminates, but @code{pthread_join} cannot be used to synchronize on
-the thread termination.
-
-A thread created in the joinable state can later be put in the detached
-thread using @code{pthread_detach}.
-
-@item schedpolicy
-Select the scheduling policy for the thread: one of @code{SCHED_OTHER}
-(regular, non-realtime scheduling), @code{SCHED_RR} (realtime,
-round-robin) or @code{SCHED_FIFO} (realtime, first-in first-out).
-The default is @code{SCHED_OTHER}.
-@c Not doc'd in our manual: FIXME.
-@c See @code{sched_setpolicy} for more information on scheduling policies.
-
-The realtime scheduling policies @code{SCHED_RR} and @code{SCHED_FIFO}
-are available only to processes with superuser privileges.
-@code{pthread_attr_setschedparam} will fail and return @code{ENOTSUP} if
-you try to set a realtime policy when you are unprivileged.
-
-The scheduling policy of a thread can be changed after creation with
-@code{pthread_setschedparam}.
-
-@item schedparam
-Change the scheduling parameter (the scheduling priority)
-for the thread. The default is 0.
-
-This attribute is not significant if the scheduling policy is
-@code{SCHED_OTHER}; it only matters for the realtime policies
-@code{SCHED_RR} and @code{SCHED_FIFO}.
-
-The scheduling priority of a thread can be changed after creation with
-@code{pthread_setschedparam}.
-
-@item inheritsched
-Choose whether the scheduling policy and scheduling parameter for the
-newly created thread are determined by the values of the
-@var{schedpolicy} and @var{schedparam} attributes (value
-@code{PTHREAD_EXPLICIT_SCHED}) or are inherited from the parent thread
-(value @code{PTHREAD_INHERIT_SCHED}). The default is
-@code{PTHREAD_EXPLICIT_SCHED}.
-
-@item scope
-Choose the scheduling contention scope for the created thread. The
-default is @code{PTHREAD_SCOPE_SYSTEM}, meaning that the threads contend
-for CPU time with all processes running on the machine. In particular,
-thread priorities are interpreted relative to the priorities of all
-other processes on the machine. The other possibility,
-@code{PTHREAD_SCOPE_PROCESS}, means that scheduling contention occurs
-only between the threads of the running process: thread priorities are
-interpreted relative to the priorities of the other threads of the
-process, regardless of the priorities of other processes.
-
-@code{PTHREAD_SCOPE_PROCESS} is not supported in LinuxThreads. If you
-try to set the scope to this value, @code{pthread_attr_setscope} will
-fail and return @code{ENOTSUP}.
-
-@item stackaddr
-Provide an address for an application managed stack. The size of the
-stack must be at least @code{PTHREAD_STACK_MIN}.
-
-@item stacksize
-Change the size of the stack created for the thread. The value defines
-the minimum stack size, in bytes.
-
-If the value exceeds the system's maximum stack size, or is smaller
-than @code{PTHREAD_STACK_MIN}, @code{pthread_attr_setstacksize} will
-fail and return @code{EINVAL}.
-
-@item stack
-Provide both the address and size of an application managed stack to
-use for the new thread. The base of the memory area is @var{stackaddr}
-with the size of the memory area, @var{stacksize}, measured in bytes.
-
-If the value of @var{stacksize} is less than @code{PTHREAD_STACK_MIN},
-or greater than the system's maximum stack size, or if the value of
-@var{stackaddr} lacks the proper alignment, @code{pthread_attr_setstack}
-will fail and return @code{EINVAL}.
-
-@item guardsize
-Change the minimum size in bytes of the guard area for the thread's
-stack. The default size is a single page. If this value is set, it
-will be rounded up to the nearest page size. If the value is set to 0,
-a guard area will not be created for this thread. The space allocated
-for the guard area is used to catch stack overflow. Therefore, when
-allocating large structures on the stack, a larger guard area may be
-required to catch a stack overflow.
-
-If the caller is managing their own stacks (if the @code{stackaddr}
-attribute has been set), then the @code{guardsize} attribute is ignored.
-
-If the value exceeds the @code{stacksize}, @code{pthread_atrr_setguardsize}
-will fail and return @code{EINVAL}.
-@end table
-
-@node Cancellation
-@section Cancellation
-
-Cancellation is the mechanism by which a thread can terminate the
-execution of another thread. More precisely, a thread can send a
-cancellation request to another thread. Depending on its settings, the
-target thread can then either ignore the request, honor it immediately,
-or defer it till it reaches a cancellation point. When threads are
-first created by @code{pthread_create}, they always defer cancellation
-requests.
-
-When a thread eventually honors a cancellation request, it behaves as if
-@code{pthread_exit(PTHREAD_CANCELED)} was called. All cleanup handlers
-are executed in reverse order, finalization functions for
-thread-specific data are called, and finally the thread stops executing.
-If the canceled thread was joinable, the return value
-@code{PTHREAD_CANCELED} is provided to whichever thread calls
-@var{pthread_join} on it. See @code{pthread_exit} for more information.
-
-Cancellation points are the points where the thread checks for pending
-cancellation requests and performs them. The POSIX threads functions
-@code{pthread_join}, @code{pthread_cond_wait},
-@code{pthread_cond_timedwait}, @code{pthread_testcancel},
-@code{sem_wait}, and @code{sigwait} are cancellation points. In
-addition, these system calls are cancellation points:
-
-@multitable @columnfractions .33 .33 .33
-@item @t{accept} @tab @t{open} @tab @t{sendmsg}
-@item @t{close} @tab @t{pause} @tab @t{sendto}
-@item @t{connect} @tab @t{read} @tab @t{system}
-@item @t{fcntl} @tab @t{recv} @tab @t{tcdrain}
-@item @t{fsync} @tab @t{recvfrom} @tab @t{wait}
-@item @t{lseek} @tab @t{recvmsg} @tab @t{waitpid}
-@item @t{msync} @tab @t{send} @tab @t{write}
-@item @t{nanosleep}
-@end multitable
-
-@noindent
-All library functions that call these functions (such as
-@code{printf}) are also cancellation points.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setcancelstate (int @var{state}, int *@var{oldstate})
-@code{pthread_setcancelstate} changes the cancellation state for the
-calling thread -- that is, whether cancellation requests are ignored or
-not. The @var{state} argument is the new cancellation state: either
-@code{PTHREAD_CANCEL_ENABLE} to enable cancellation, or
-@code{PTHREAD_CANCEL_DISABLE} to disable cancellation (cancellation
-requests are ignored).
-
-If @var{oldstate} is not @code{NULL}, the previous cancellation state is
-stored in the location pointed to by @var{oldstate}, and can thus be
-restored later by another call to @code{pthread_setcancelstate}.
-
-If the @var{state} argument is not @code{PTHREAD_CANCEL_ENABLE} or
-@code{PTHREAD_CANCEL_DISABLE}, @code{pthread_setcancelstate} fails and
-returns @code{EINVAL}. Otherwise it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setcanceltype (int @var{type}, int *@var{oldtype})
-@code{pthread_setcanceltype} changes the type of responses to
-cancellation requests for the calling thread: asynchronous (immediate)
-or deferred. The @var{type} argument is the new cancellation type:
-either @code{PTHREAD_CANCEL_ASYNCHRONOUS} to cancel the calling thread
-as soon as the cancellation request is received, or
-@code{PTHREAD_CANCEL_DEFERRED} to keep the cancellation request pending
-until the next cancellation point. If @var{oldtype} is not @code{NULL},
-the previous cancellation state is stored in the location pointed to by
-@var{oldtype}, and can thus be restored later by another call to
-@code{pthread_setcanceltype}.
-
-If the @var{type} argument is not @code{PTHREAD_CANCEL_DEFERRED} or
-@code{PTHREAD_CANCEL_ASYNCHRONOUS}, @code{pthread_setcanceltype} fails
-and returns @code{EINVAL}. Otherwise it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_testcancel (@var{void})
-@code{pthread_testcancel} does nothing except testing for pending
-cancellation and executing it. Its purpose is to introduce explicit
-checks for cancellation in long sequences of code that do not call
-cancellation point functions otherwise.
-@end deftypefun
-
-@node Cleanup Handlers
-@section Cleanup Handlers
-
-Cleanup handlers are functions that get called when a thread terminates,
-either by calling @code{pthread_exit} or because of
-cancellation. Cleanup handlers are installed and removed following a
-stack-like discipline.
-
-The purpose of cleanup handlers is to free the resources that a thread
-may hold at the time it terminates. In particular, if a thread exits or
-is canceled while it owns a locked mutex, the mutex will remain locked
-forever and prevent other threads from executing normally. The best way
-to avoid this is, just before locking the mutex, to install a cleanup
-handler whose effect is to unlock the mutex. Cleanup handlers can be
-used similarly to free blocks allocated with @code{malloc} or close file
-descriptors on thread termination.
-
-Here is how to lock a mutex @var{mut} in such a way that it will be
-unlocked if the thread is canceled while @var{mut} is locked:
-
-@smallexample
-pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_mutex_unlock(&mut);
-pthread_cleanup_pop(0);
-@end smallexample
-
-Equivalently, the last two lines can be replaced by
-
-@smallexample
-pthread_cleanup_pop(1);
-@end smallexample
-
-Notice that the code above is safe only in deferred cancellation mode
-(see @code{pthread_setcanceltype}). In asynchronous cancellation mode, a
-cancellation can occur between @code{pthread_cleanup_push} and
-@code{pthread_mutex_lock}, or between @code{pthread_mutex_unlock} and
-@code{pthread_cleanup_pop}, resulting in both cases in the thread trying
-to unlock a mutex not locked by the current thread. This is the main
-reason why asynchronous cancellation is difficult to use.
-
-If the code above must also work in asynchronous cancellation mode,
-then it must switch to deferred mode for locking and unlocking the
-mutex:
-
-@smallexample
-pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
-pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_cleanup_pop(1);
-pthread_setcanceltype(oldtype, NULL);
-@end smallexample
-
-The code above can be rewritten in a more compact and efficient way,
-using the non-portable functions @code{pthread_cleanup_push_defer_np}
-and @code{pthread_cleanup_pop_restore_np}:
-
-@smallexample
-pthread_cleanup_push_defer_np(pthread_mutex_unlock, (void *) &mut);
-pthread_mutex_lock(&mut);
-/* do some work */
-pthread_cleanup_pop_restore_np(1);
-@end smallexample
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_cleanup_push (void (*@var{routine}) (void *), void *@var{arg})
-
-@code{pthread_cleanup_push} installs the @var{routine} function with
-argument @var{arg} as a cleanup handler. From this point on to the
-matching @code{pthread_cleanup_pop}, the function @var{routine} will be
-called with arguments @var{arg} when the thread terminates, either
-through @code{pthread_exit} or by cancellation. If several cleanup
-handlers are active at that point, they are called in LIFO order: the
-most recently installed handler is called first.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun void pthread_cleanup_pop (int @var{execute})
-@code{pthread_cleanup_pop} removes the most recently installed cleanup
-handler. If the @var{execute} argument is not 0, it also executes the
-handler, by calling the @var{routine} function with arguments
-@var{arg}. If the @var{execute} argument is 0, the handler is only
-removed but not executed.
-@end deftypefun
-
-Matching pairs of @code{pthread_cleanup_push} and
-@code{pthread_cleanup_pop} must occur in the same function, at the same
-level of block nesting. Actually, @code{pthread_cleanup_push} and
-@code{pthread_cleanup_pop} are macros, and the expansion of
-@code{pthread_cleanup_push} introduces an open brace @code{@{} with the
-matching closing brace @code{@}} being introduced by the expansion of the
-matching @code{pthread_cleanup_pop}.
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_cleanup_push_defer_np (void (*@var{routine}) (void *), void *@var{arg})
-@code{pthread_cleanup_push_defer_np} is a non-portable extension that
-combines @code{pthread_cleanup_push} and @code{pthread_setcanceltype}.
-It pushes a cleanup handler just as @code{pthread_cleanup_push} does,
-but also saves the current cancellation type and sets it to deferred
-cancellation. This ensures that the cleanup mechanism is effective even
-if the thread was initially in asynchronous cancellation mode.
-@end deftypefun
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_cleanup_pop_restore_np (int @var{execute})
-@code{pthread_cleanup_pop_restore_np} pops a cleanup handler introduced
-by @code{pthread_cleanup_push_defer_np}, and restores the cancellation
-type to its value at the time @code{pthread_cleanup_push_defer_np} was
-called.
-@end deftypefun
-
-@code{pthread_cleanup_push_defer_np} and
-@code{pthread_cleanup_pop_restore_np} must occur in matching pairs, at
-the same level of block nesting.
-
-The sequence
-
-@smallexample
-pthread_cleanup_push_defer_np(routine, arg);
-...
-pthread_cleanup_pop_restore_np(execute);
-@end smallexample
-
-@noindent
-is functionally equivalent to (but more compact and efficient than)
-
-@smallexample
-@{
- int oldtype;
- pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
- pthread_cleanup_push(routine, arg);
- ...
- pthread_cleanup_pop(execute);
- pthread_setcanceltype(oldtype, NULL);
-@}
-@end smallexample
-
-
-@node Mutexes
-@section Mutexes
-
-A mutex is a MUTual EXclusion device, and is useful for protecting
-shared data structures from concurrent modifications, and implementing
-critical sections and monitors.
-
-A mutex has two possible states: unlocked (not owned by any thread),
-and locked (owned by one thread). A mutex can never be owned by two
-different threads simultaneously. A thread attempting to lock a mutex
-that is already locked by another thread is suspended until the owning
-thread unlocks the mutex first.
-
-None of the mutex functions is a cancellation point, not even
-@code{pthread_mutex_lock}, in spite of the fact that it can suspend a
-thread for arbitrary durations. This way, the status of mutexes at
-cancellation points is predictable, allowing cancellation handlers to
-unlock precisely those mutexes that need to be unlocked before the
-thread stops executing. Consequently, threads using deferred
-cancellation should never hold a mutex for extended periods of time.
-
-It is not safe to call mutex functions from a signal handler. In
-particular, calling @code{pthread_mutex_lock} or
-@code{pthread_mutex_unlock} from a signal handler may deadlock the
-calling thread.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_init (pthread_mutex_t *@var{mutex}, const pthread_mutexattr_t *@var{mutexattr})
-
-@code{pthread_mutex_init} initializes the mutex object pointed to by
-@var{mutex} according to the mutex attributes specified in @var{mutexattr}.
-If @var{mutexattr} is @code{NULL}, default attributes are used instead.
-
-The LinuxThreads implementation supports only one mutex attribute,
-the @var{mutex type}, which is either ``fast'', ``recursive'', or
-``error checking''. The type of a mutex determines whether
-it can be locked again by a thread that already owns it.
-The default type is ``fast''.
-
-Variables of type @code{pthread_mutex_t} can also be initialized
-statically, using the constants @code{PTHREAD_MUTEX_INITIALIZER} (for
-timed mutexes), @code{PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP} (for
-recursive mutexes), @code{PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP}
-(for fast mutexes(, and @code{PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP}
-(for error checking mutexes).
-
-@code{pthread_mutex_init} always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_lock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_lock} locks the given mutex. If the mutex is
-currently unlocked, it becomes locked and owned by the calling thread,
-and @code{pthread_mutex_lock} returns immediately. If the mutex is
-already locked by another thread, @code{pthread_mutex_lock} suspends the
-calling thread until the mutex is unlocked.
-
-If the mutex is already locked by the calling thread, the behavior of
-@code{pthread_mutex_lock} depends on the type of the mutex. If the mutex
-is of the ``fast'' type, the calling thread is suspended. It will
-remain suspended forever, because no other thread can unlock the mutex.
-If the mutex is of the ``error checking'' type, @code{pthread_mutex_lock}
-returns immediately with the error code @code{EDEADLK}. If the mutex is
-of the ``recursive'' type, @code{pthread_mutex_lock} succeeds and
-returns immediately, recording the number of times the calling thread
-has locked the mutex. An equal number of @code{pthread_mutex_unlock}
-operations must be performed before the mutex returns to the unlocked
-state.
-@c This doesn't discuss PTHREAD_MUTEX_TIMED_NP mutex attributes. FIXME
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_trylock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_trylock} behaves identically to
-@code{pthread_mutex_lock}, except that it does not block the calling
-thread if the mutex is already locked by another thread (or by the
-calling thread in the case of a ``fast'' mutex). Instead,
-@code{pthread_mutex_trylock} returns immediately with the error code
-@code{EBUSY}.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_timedlock (pthread_mutex_t *@var{mutex}, const struct timespec *@var{abstime})
-The @code{pthread_mutex_timedlock} is similar to the
-@code{pthread_mutex_lock} function but instead of blocking for in
-indefinite time if the mutex is locked by another thread, it returns
-when the time specified in @var{abstime} is reached.
-
-This function can only be used on standard (``timed'') and ``error
-checking'' mutexes. It behaves just like @code{pthread_mutex_lock} for
-all other types.
-
-If the mutex is successfully locked, the function returns zero. If the
-time specified in @var{abstime} is reached without the mutex being locked,
-@code{ETIMEDOUT} is returned.
-
-This function was introduced in the POSIX.1d revision of the POSIX standard.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_unlock (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_unlock} unlocks the given mutex. The mutex is
-assumed to be locked and owned by the calling thread on entrance to
-@code{pthread_mutex_unlock}. If the mutex is of the ``fast'' type,
-@code{pthread_mutex_unlock} always returns it to the unlocked state. If
-it is of the ``recursive'' type, it decrements the locking count of the
-mutex (number of @code{pthread_mutex_lock} operations performed on it by
-the calling thread), and only when this count reaches zero is the mutex
-actually unlocked.
-
-On ``error checking'' mutexes, @code{pthread_mutex_unlock} actually
-checks at run-time that the mutex is locked on entrance, and that it was
-locked by the same thread that is now calling
-@code{pthread_mutex_unlock}. If these conditions are not met,
-@code{pthread_mutex_unlock} returns @code{EPERM}, and the mutex remains
-unchanged. ``Fast'' and ``recursive'' mutexes perform no such checks,
-thus allowing a locked mutex to be unlocked by a thread other than its
-owner. This is non-portable behavior and must not be relied upon.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutex_destroy (pthread_mutex_t *@var{mutex})
-@code{pthread_mutex_destroy} destroys a mutex object, freeing the
-resources it might hold. The mutex must be unlocked on entrance. In the
-LinuxThreads implementation, no resources are associated with mutex
-objects, thus @code{pthread_mutex_destroy} actually does nothing except
-checking that the mutex is unlocked.
-
-If the mutex is locked by some thread, @code{pthread_mutex_destroy}
-returns @code{EBUSY}. Otherwise it returns 0.
-@end deftypefun
-
-If any of the above functions (except @code{pthread_mutex_init})
-is applied to an uninitialized mutex, they will simply return
-@code{EINVAL} and do nothing.
-
-A shared global variable @var{x} can be protected by a mutex as follows:
-
-@smallexample
-int x;
-pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
-@end smallexample
-
-All accesses and modifications to @var{x} should be bracketed by calls to
-@code{pthread_mutex_lock} and @code{pthread_mutex_unlock} as follows:
-
-@smallexample
-pthread_mutex_lock(&mut);
-/* operate on x */
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Mutex attributes can be specified at mutex creation time, by passing a
-mutex attribute object as second argument to @code{pthread_mutex_init}.
-Passing @code{NULL} is equivalent to passing a mutex attribute object
-with all attributes set to their default values.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_init (pthread_mutexattr_t *@var{attr})
-@code{pthread_mutexattr_init} initializes the mutex attribute object
-@var{attr} and fills it with default values for the attributes.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_destroy (pthread_mutexattr_t *@var{attr})
-@code{pthread_mutexattr_destroy} destroys a mutex attribute object,
-which must not be reused until it is
-reinitialized. @code{pthread_mutexattr_destroy} does nothing in the
-LinuxThreads implementation.
-
-This function always returns 0.
-@end deftypefun
-
-LinuxThreads supports only one mutex attribute: the mutex type, which is
-either @code{PTHREAD_MUTEX_ADAPTIVE_NP} for ``fast'' mutexes,
-@code{PTHREAD_MUTEX_RECURSIVE_NP} for ``recursive'' mutexes,
-@code{PTHREAD_MUTEX_TIMED_NP} for ``timed'' mutexes, or
-@code{PTHREAD_MUTEX_ERRORCHECK_NP} for ``error checking'' mutexes. As
-the @code{NP} suffix indicates, this is a non-portable extension to the
-POSIX standard and should not be employed in portable programs.
-
-The mutex type determines what happens if a thread attempts to lock a
-mutex it already owns with @code{pthread_mutex_lock}. If the mutex is of
-the ``fast'' type, @code{pthread_mutex_lock} simply suspends the calling
-thread forever. If the mutex is of the ``error checking'' type,
-@code{pthread_mutex_lock} returns immediately with the error code
-@code{EDEADLK}. If the mutex is of the ``recursive'' type, the call to
-@code{pthread_mutex_lock} returns immediately with a success return
-code. The number of times the thread owning the mutex has locked it is
-recorded in the mutex. The owning thread must call
-@code{pthread_mutex_unlock} the same number of times before the mutex
-returns to the unlocked state.
-
-The default mutex type is ``timed'', that is, @code{PTHREAD_MUTEX_TIMED_NP}.
-@c This doesn't describe how a ``timed'' mutex behaves. FIXME
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_settype (pthread_mutexattr_t *@var{attr}, int @var{type})
-@code{pthread_mutexattr_settype} sets the mutex type attribute in
-@var{attr} to the value specified by @var{type}.
-
-If @var{type} is not @code{PTHREAD_MUTEX_ADAPTIVE_NP},
-@code{PTHREAD_MUTEX_RECURSIVE_NP}, @code{PTHREAD_MUTEX_TIMED_NP}, or
-@code{PTHREAD_MUTEX_ERRORCHECK_NP}, this function will return
-@code{EINVAL} and leave @var{attr} unchanged.
-
-The standard Unix98 identifiers @code{PTHREAD_MUTEX_DEFAULT},
-@code{PTHREAD_MUTEX_NORMAL}, @code{PTHREAD_MUTEX_RECURSIVE},
-and @code{PTHREAD_MUTEX_ERRORCHECK} are also permitted.
-
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_mutexattr_gettype (const pthread_mutexattr_t *@var{attr}, int *@var{type})
-@code{pthread_mutexattr_gettype} retrieves the current value of the
-mutex type attribute in @var{attr} and stores it in the location pointed
-to by @var{type}.
-
-This function always returns 0.
-@end deftypefun
-
-@node Condition Variables
-@section Condition Variables
-
-A condition (short for ``condition variable'') is a synchronization
-device that allows threads to suspend execution until some predicate on
-shared data is satisfied. The basic operations on conditions are: signal
-the condition (when the predicate becomes true), and wait for the
-condition, suspending the thread execution until another thread signals
-the condition.
-
-A condition variable must always be associated with a mutex, to avoid
-the race condition where a thread prepares to wait on a condition
-variable and another thread signals the condition just before the first
-thread actually waits on it.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_init (pthread_cond_t *@var{cond}, pthread_condattr_t *cond_@var{attr})
-
-@code{pthread_cond_init} initializes the condition variable @var{cond},
-using the condition attributes specified in @var{cond_attr}, or default
-attributes if @var{cond_attr} is @code{NULL}. The LinuxThreads
-implementation supports no attributes for conditions, hence the
-@var{cond_attr} parameter is actually ignored.
-
-Variables of type @code{pthread_cond_t} can also be initialized
-statically, using the constant @code{PTHREAD_COND_INITIALIZER}.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_signal (pthread_cond_t *@var{cond})
-@code{pthread_cond_signal} restarts one of the threads that are waiting
-on the condition variable @var{cond}. If no threads are waiting on
-@var{cond}, nothing happens. If several threads are waiting on
-@var{cond}, exactly one is restarted, but it is not specified which.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_broadcast (pthread_cond_t *@var{cond})
-@code{pthread_cond_broadcast} restarts all the threads that are waiting
-on the condition variable @var{cond}. Nothing happens if no threads are
-waiting on @var{cond}.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_wait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex})
-@code{pthread_cond_wait} atomically unlocks the @var{mutex} (as per
-@code{pthread_unlock_mutex}) and waits for the condition variable
-@var{cond} to be signaled. The thread execution is suspended and does
-not consume any CPU time until the condition variable is signaled. The
-@var{mutex} must be locked by the calling thread on entrance to
-@code{pthread_cond_wait}. Before returning to the calling thread,
-@code{pthread_cond_wait} re-acquires @var{mutex} (as per
-@code{pthread_lock_mutex}).
-
-Unlocking the mutex and suspending on the condition variable is done
-atomically. Thus, if all threads always acquire the mutex before
-signaling the condition, this guarantees that the condition cannot be
-signaled (and thus ignored) between the time a thread locks the mutex
-and the time it waits on the condition variable.
-
-This function always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_timedwait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex}, const struct timespec *@var{abstime})
-@code{pthread_cond_timedwait} atomically unlocks @var{mutex} and waits
-on @var{cond}, as @code{pthread_cond_wait} does, but it also bounds the
-duration of the wait. If @var{cond} has not been signaled before time
-@var{abstime}, the mutex @var{mutex} is re-acquired and
-@code{pthread_cond_timedwait} returns the error code @code{ETIMEDOUT}.
-The wait can also be interrupted by a signal; in that case
-@code{pthread_cond_timedwait} returns @code{EINTR}.
-
-The @var{abstime} parameter specifies an absolute time, with the same
-origin as @code{time} and @code{gettimeofday}: an @var{abstime} of 0
-corresponds to 00:00:00 GMT, January 1, 1970.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_cond_destroy (pthread_cond_t *@var{cond})
-@code{pthread_cond_destroy} destroys the condition variable @var{cond},
-freeing the resources it might hold. If any threads are waiting on the
-condition variable, @code{pthread_cond_destroy} leaves @var{cond}
-untouched and returns @code{EBUSY}. Otherwise it returns 0, and
-@var{cond} must not be used again until it is reinitialized.
-
-In the LinuxThreads implementation, no resources are associated with
-condition variables, so @code{pthread_cond_destroy} actually does
-nothing.
-@end deftypefun
-
-@code{pthread_cond_wait} and @code{pthread_cond_timedwait} are
-cancellation points. If a thread is canceled while suspended in one of
-these functions, the thread immediately resumes execution, relocks the
-mutex specified by @var{mutex}, and finally executes the cancellation.
-Consequently, cleanup handlers are assured that @var{mutex} is locked
-when they are called.
-
-It is not safe to call the condition variable functions from a signal
-handler. In particular, calling @code{pthread_cond_signal} or
-@code{pthread_cond_broadcast} from a signal handler may deadlock the
-calling thread.
-
-Consider two shared variables @var{x} and @var{y}, protected by the
-mutex @var{mut}, and a condition variable @var{cond} that is to be
-signaled whenever @var{x} becomes greater than @var{y}.
-
-@smallexample
-int x,y;
-pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
-pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
-@end smallexample
-
-Waiting until @var{x} is greater than @var{y} is performed as follows:
-
-@smallexample
-pthread_mutex_lock(&mut);
-while (x <= y) @{
- pthread_cond_wait(&cond, &mut);
-@}
-/* operate on x and y */
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Modifications on @var{x} and @var{y} that may cause @var{x} to become greater than
-@var{y} should signal the condition if needed:
-
-@smallexample
-pthread_mutex_lock(&mut);
-/* modify x and y */
-if (x > y) pthread_cond_broadcast(&cond);
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-If it can be proved that at most one waiting thread needs to be waken
-up (for instance, if there are only two threads communicating through
-@var{x} and @var{y}), @code{pthread_cond_signal} can be used as a slightly more
-efficient alternative to @code{pthread_cond_broadcast}. In doubt, use
-@code{pthread_cond_broadcast}.
-
-To wait for @var{x} to becomes greater than @var{y} with a timeout of 5
-seconds, do:
-
-@smallexample
-struct timeval now;
-struct timespec timeout;
-int retcode;
-
-pthread_mutex_lock(&mut);
-gettimeofday(&now);
-timeout.tv_sec = now.tv_sec + 5;
-timeout.tv_nsec = now.tv_usec * 1000;
-retcode = 0;
-while (x <= y && retcode != ETIMEDOUT) @{
- retcode = pthread_cond_timedwait(&cond, &mut, &timeout);
-@}
-if (retcode == ETIMEDOUT) @{
- /* timeout occurred */
-@} else @{
- /* operate on x and y */
-@}
-pthread_mutex_unlock(&mut);
-@end smallexample
-
-Condition attributes can be specified at condition creation time, by
-passing a condition attribute object as second argument to
-@code{pthread_cond_init}. Passing @code{NULL} is equivalent to passing
-a condition attribute object with all attributes set to their default
-values.
-
-The LinuxThreads implementation supports no attributes for
-conditions. The functions on condition attributes are included only for
-compliance with the POSIX standard.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_condattr_init (pthread_condattr_t *@var{attr})
-@deftypefunx int pthread_condattr_destroy (pthread_condattr_t *@var{attr})
-@code{pthread_condattr_init} initializes the condition attribute object
-@var{attr} and fills it with default values for the attributes.
-@code{pthread_condattr_destroy} destroys the condition attribute object
-@var{attr}.
-
-Both functions do nothing in the LinuxThreads implementation.
-
-@code{pthread_condattr_init} and @code{pthread_condattr_destroy} always
-return 0.
-@end deftypefun
-
-@node POSIX Semaphores
-@section POSIX Semaphores
-
-@vindex SEM_VALUE_MAX
-Semaphores are counters for resources shared between threads. The
-basic operations on semaphores are: increment the counter atomically,
-and wait until the counter is non-null and decrement it atomically.
-
-Semaphores have a maximum value past which they cannot be incremented.
-The macro @code{SEM_VALUE_MAX} is defined to be this maximum value. In
-the GNU C library, @code{SEM_VALUE_MAX} is equal to @code{INT_MAX}
-(@pxref{Range of Type}), but it may be much smaller on other systems.
-
-The pthreads library implements POSIX 1003.1b semaphores. These should
-not be confused with System V semaphores (@code{ipc}, @code{semctl} and
-@code{semop}).
-@c !!! SysV IPC is not doc'd at all in our manual
-
-All the semaphore functions and macros are defined in @file{semaphore.h}.
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_init (sem_t *@var{sem}, int @var{pshared}, unsigned int @var{value})
-@code{sem_init} initializes the semaphore object pointed to by
-@var{sem}. The count associated with the semaphore is set initially to
-@var{value}. The @var{pshared} argument indicates whether the semaphore
-is local to the current process (@var{pshared} is zero) or is to be
-shared between several processes (@var{pshared} is not zero).
-
-On success @code{sem_init} returns 0. On failure it returns -1 and sets
-@var{errno} to one of the following values:
-
-@table @code
-@item EINVAL
-@var{value} exceeds the maximal counter value @code{SEM_VALUE_MAX}
-
-@item ENOSYS
-@var{pshared} is not zero. LinuxThreads currently does not support
-process-shared semaphores. (This will eventually change.)
-@end table
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_destroy (sem_t * @var{sem})
-@code{sem_destroy} destroys a semaphore object, freeing the resources it
-might hold. If any threads are waiting on the semaphore when
-@code{sem_destroy} is called, it fails and sets @var{errno} to
-@code{EBUSY}.
-
-In the LinuxThreads implementation, no resources are associated with
-semaphore objects, thus @code{sem_destroy} actually does nothing except
-checking that no thread is waiting on the semaphore. This will change
-when process-shared semaphores are implemented.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_wait (sem_t * @var{sem})
-@code{sem_wait} suspends the calling thread until the semaphore pointed
-to by @var{sem} has non-zero count. It then atomically decreases the
-semaphore count.
-
-@code{sem_wait} is a cancellation point. It always returns 0.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_trywait (sem_t * @var{sem})
-@code{sem_trywait} is a non-blocking variant of @code{sem_wait}. If the
-semaphore pointed to by @var{sem} has non-zero count, the count is
-atomically decreased and @code{sem_trywait} immediately returns 0. If
-the semaphore count is zero, @code{sem_trywait} immediately returns -1
-and sets errno to @code{EAGAIN}.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_post (sem_t * @var{sem})
-@code{sem_post} atomically increases the count of the semaphore pointed to
-by @var{sem}. This function never blocks.
-
-@c !!! This para appears not to agree with the code.
-On processors supporting atomic compare-and-swap (Intel 486, Pentium and
-later, Alpha, PowerPC, MIPS II, Motorola 68k, Ultrasparc), the
-@code{sem_post} function is can safely be called from signal handlers.
-This is the only thread synchronization function provided by POSIX
-threads that is async-signal safe. On the Intel 386 and earlier Sparc
-chips, the current LinuxThreads implementation of @code{sem_post} is not
-async-signal safe, because the hardware does not support the required
-atomic operations.
-
-@code{sem_post} always succeeds and returns 0, unless the semaphore
-count would exceed @code{SEM_VALUE_MAX} after being incremented. In
-that case @code{sem_post} returns -1 and sets @var{errno} to
-@code{EINVAL}. The semaphore count is left unchanged.
-@end deftypefun
-
-@comment semaphore.h
-@comment POSIX
-@deftypefun int sem_getvalue (sem_t * @var{sem}, int * @var{sval})
-@code{sem_getvalue} stores in the location pointed to by @var{sval} the
-current count of the semaphore @var{sem}. It always returns 0.
-@end deftypefun
-
-@node Thread-Specific Data
-@section Thread-Specific Data
-
-Programs often need global or static variables that have different
-values in different threads. Since threads share one memory space, this
-cannot be achieved with regular variables. Thread-specific data is the
-POSIX threads answer to this need.
-
-Each thread possesses a private memory block, the thread-specific data
-area, or TSD area for short. This area is indexed by TSD keys. The TSD
-area associates values of type @code{void *} to TSD keys. TSD keys are
-common to all threads, but the value associated with a given TSD key can
-be different in each thread.
-
-For concreteness, the TSD areas can be viewed as arrays of @code{void *}
-pointers, TSD keys as integer indices into these arrays, and the value
-of a TSD key as the value of the corresponding array element in the
-calling thread.
-
-When a thread is created, its TSD area initially associates @code{NULL}
-with all keys.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_key_create (pthread_key_t *@var{key}, void (*destr_function) (void *))
-@code{pthread_key_create} allocates a new TSD key. The key is stored in
-the location pointed to by @var{key}. There is a limit of
-@code{PTHREAD_KEYS_MAX} on the number of keys allocated at a given
-time. The value initially associated with the returned key is
-@code{NULL} in all currently executing threads.
-
-The @var{destr_function} argument, if not @code{NULL}, specifies a
-destructor function associated with the key. When a thread terminates
-via @code{pthread_exit} or by cancellation, @var{destr_function} is
-called on the value associated with the key in that thread. The
-@var{destr_function} is not called if a key is deleted with
-@code{pthread_key_delete} or a value is changed with
-@code{pthread_setspecific}. The order in which destructor functions are
-called at thread termination time is unspecified.
-
-Before the destructor function is called, the @code{NULL} value is
-associated with the key in the current thread. A destructor function
-might, however, re-associate non-@code{NULL} values to that key or some
-other key. To deal with this, if after all the destructors have been
-called for all non-@code{NULL} values, there are still some
-non-@code{NULL} values with associated destructors, then the process is
-repeated. The LinuxThreads implementation stops the process after
-@code{PTHREAD_DESTRUCTOR_ITERATIONS} iterations, even if some
-non-@code{NULL} values with associated descriptors remain. Other
-implementations may loop indefinitely.
-
-@code{pthread_key_create} returns 0 unless @code{PTHREAD_KEYS_MAX} keys
-have already been allocated, in which case it fails and returns
-@code{EAGAIN}.
-@end deftypefun
-
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_key_delete (pthread_key_t @var{key})
-@code{pthread_key_delete} deallocates a TSD key. It does not check
-whether non-@code{NULL} values are associated with that key in the
-currently executing threads, nor call the destructor function associated
-with the key.
-
-If there is no such key @var{key}, it returns @code{EINVAL}. Otherwise
-it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setspecific (pthread_key_t @var{key}, const void *@var{pointer})
-@code{pthread_setspecific} changes the value associated with @var{key}
-in the calling thread, storing the given @var{pointer} instead.
-
-If there is no such key @var{key}, it returns @code{EINVAL}. Otherwise
-it returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun {void *} pthread_getspecific (pthread_key_t @var{key})
-@code{pthread_getspecific} returns the value currently associated with
-@var{key} in the calling thread.
-
-If there is no such key @var{key}, it returns @code{NULL}.
-@end deftypefun
-
-The following code fragment allocates a thread-specific array of 100
-characters, with automatic reclaimation at thread exit:
-
-@smallexample
-/* Key for the thread-specific buffer */
-static pthread_key_t buffer_key;
-
-/* Once-only initialisation of the key */
-static pthread_once_t buffer_key_once = PTHREAD_ONCE_INIT;
-
-/* Allocate the thread-specific buffer */
-void buffer_alloc(void)
-@{
- pthread_once(&buffer_key_once, buffer_key_alloc);
- pthread_setspecific(buffer_key, malloc(100));
-@}
-
-/* Return the thread-specific buffer */
-char * get_buffer(void)
-@{
- return (char *) pthread_getspecific(buffer_key);
-@}
-
-/* Allocate the key */
-static void buffer_key_alloc()
-@{
- pthread_key_create(&buffer_key, buffer_destroy);
-@}
-
-/* Free the thread-specific buffer */
-static void buffer_destroy(void * buf)
-@{
- free(buf);
-@}
-@end smallexample
-
-@node Threads and Signal Handling
-@section Threads and Signal Handling
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_sigmask (int @var{how}, const sigset_t *@var{newmask}, sigset_t *@var{oldmask})
-@code{pthread_sigmask} changes the signal mask for the calling thread as
-described by the @var{how} and @var{newmask} arguments. If @var{oldmask}
-is not @code{NULL}, the previous signal mask is stored in the location
-pointed to by @var{oldmask}.
-
-The meaning of the @var{how} and @var{newmask} arguments is the same as
-for @code{sigprocmask}. If @var{how} is @code{SIG_SETMASK}, the signal
-mask is set to @var{newmask}. If @var{how} is @code{SIG_BLOCK}, the
-signals specified to @var{newmask} are added to the current signal mask.
-If @var{how} is @code{SIG_UNBLOCK}, the signals specified to
-@var{newmask} are removed from the current signal mask.
-
-Recall that signal masks are set on a per-thread basis, but signal
-actions and signal handlers, as set with @code{sigaction}, are shared
-between all threads.
-
-The @code{pthread_sigmask} function returns 0 on success, and one of the
-following error codes on error:
-@table @code
-@item EINVAL
-@var{how} is not one of @code{SIG_SETMASK}, @code{SIG_BLOCK}, or @code{SIG_UNBLOCK}
-
-@item EFAULT
-@var{newmask} or @var{oldmask} point to invalid addresses
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_kill (pthread_t @var{thread}, int @var{signo})
-@code{pthread_kill} sends signal number @var{signo} to the thread
-@var{thread}. The signal is delivered and handled as described in
-@ref{Signal Handling}.
-
-@code{pthread_kill} returns 0 on success, one of the following error codes
-on error:
-@table @code
-@item EINVAL
-@var{signo} is not a valid signal number
-
-@item ESRCH
-The thread @var{thread} does not exist (e.g. it has already terminated)
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int sigwait (const sigset_t *@var{set}, int *@var{sig})
-@code{sigwait} suspends the calling thread until one of the signals in
-@var{set} is delivered to the calling thread. It then stores the number
-of the signal received in the location pointed to by @var{sig} and
-returns. The signals in @var{set} must be blocked and not ignored on
-entrance to @code{sigwait}. If the delivered signal has a signal handler
-function attached, that function is @emph{not} called.
-
-@code{sigwait} is a cancellation point. It always returns 0.
-@end deftypefun
-
-For @code{sigwait} to work reliably, the signals being waited for must be
-blocked in all threads, not only in the calling thread, since
-otherwise the POSIX semantics for signal delivery do not guarantee
-that it's the thread doing the @code{sigwait} that will receive the signal.
-The best way to achieve this is block those signals before any threads
-are created, and never unblock them in the program other than by
-calling @code{sigwait}.
-
-Signal handling in LinuxThreads departs significantly from the POSIX
-standard. According to the standard, ``asynchronous'' (external) signals
-are addressed to the whole process (the collection of all threads),
-which then delivers them to one particular thread. The thread that
-actually receives the signal is any thread that does not currently block
-the signal.
-
-In LinuxThreads, each thread is actually a kernel process with its own
-PID, so external signals are always directed to one particular thread.
-If, for instance, another thread is blocked in @code{sigwait} on that
-signal, it will not be restarted.
-
-The LinuxThreads implementation of @code{sigwait} installs dummy signal
-handlers for the signals in @var{set} for the duration of the
-wait. Since signal handlers are shared between all threads, other
-threads must not attach their own signal handlers to these signals, or
-alternatively they should all block these signals (which is recommended
-anyway).
-
-@node Threads and Fork
-@section Threads and Fork
-
-It's not intuitively obvious what should happen when a multi-threaded POSIX
-process calls @code{fork}. Not only are the semantics tricky, but you may
-need to write code that does the right thing at fork time even if that code
-doesn't use the @code{fork} function. Moreover, you need to be aware of
-interaction between @code{fork} and some library features like
-@code{pthread_once} and stdio streams.
-
-When @code{fork} is called by one of the threads of a process, it creates a new
-process which is copy of the calling process. Effectively, in addition to
-copying certain system objects, the function takes a snapshot of the memory
-areas of the parent process, and creates identical areas in the child.
-To make matters more complicated, with threads it's possible for two or more
-threads to concurrently call fork to create two or more child processes.
-
-The child process has a copy of the address space of the parent, but it does
-not inherit any of its threads. Execution of the child process is carried out
-by a new thread which returns from @code{fork} function with a return value of
-zero; it is the only thread in the child process. Because threads are not
-inherited across fork, issues arise. At the time of the call to @code{fork},
-threads in the parent process other than the one calling @code{fork} may have
-been executing critical regions of code. As a result, the child process may
-get a copy of objects that are not in a well-defined state. This potential
-problem affects all components of the program.
-
-Any program component which will continue being used in a child process must
-correctly handle its state during @code{fork}. For this purpose, the POSIX
-interface provides the special function @code{pthread_atfork} for installing
-pointers to handler functions which are called from within @code{fork}.
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_atfork (void (*@var{prepare})(void), void (*@var{parent})(void), void (*@var{child})(void))
-
-@code{pthread_atfork} registers handler functions to be called just
-before and just after a new process is created with @code{fork}. The
-@var{prepare} handler will be called from the parent process, just
-before the new process is created. The @var{parent} handler will be
-called from the parent process, just before @code{fork} returns. The
-@var{child} handler will be called from the child process, just before
-@code{fork} returns.
-
-@code{pthread_atfork} returns 0 on success and a non-zero error code on
-error.
-
-One or more of the three handlers @var{prepare}, @var{parent} and
-@var{child} can be given as @code{NULL}, meaning that no handler needs
-to be called at the corresponding point.
-
-@code{pthread_atfork} can be called several times to install several
-sets of handlers. At @code{fork} time, the @var{prepare} handlers are
-called in LIFO order (last added with @code{pthread_atfork}, first
-called before @code{fork}), while the @var{parent} and @var{child}
-handlers are called in FIFO order (first added, first called).
-
-If there is insufficient memory available to register the handlers,
-@code{pthread_atfork} fails and returns @code{ENOMEM}. Otherwise it
-returns 0.
-
-The functions @code{fork} and @code{pthread_atfork} must not be regarded as
-reentrant from the context of the handlers. That is to say, if a
-@code{pthread_atfork} handler invoked from within @code{fork} calls
-@code{pthread_atfork} or @code{fork}, the behavior is undefined.
-
-Registering a triplet of handlers is an atomic operation with respect to fork.
-If new handlers are registered at about the same time as a fork occurs, either
-all three handlers will be called, or none of them will be called.
-
-The handlers are inherited by the child process, and there is no
-way to remove them, short of using @code{exec} to load a new
-pocess image.
-
-@end deftypefun
-
-To understand the purpose of @code{pthread_atfork}, recall that
-@code{fork} duplicates the whole memory space, including mutexes in
-their current locking state, but only the calling thread: other threads
-are not running in the child process. The mutexes are not usable after
-the @code{fork} and must be initialized with @code{pthread_mutex_init}
-in the child process. This is a limitation of the current
-implementation and might or might not be present in future versions.
-
-To avoid this, install handlers with @code{pthread_atfork} as follows: have the
-@var{prepare} handler lock the mutexes (in locking order), and the
-@var{parent} handler unlock the mutexes. The @var{child} handler should reset
-the mutexes using @code{pthread_mutex_init}, as well as any other
-synchronization objects such as condition variables.
-
-Locking the global mutexes before the fork ensures that all other threads are
-locked out of the critical regions of code protected by those mutexes. Thus
-when @code{fork} takes a snapshot of the parent's address space, that snapshot
-will copy valid, stable data. Resetting the synchronization objects in the
-child process will ensure they are properly cleansed of any artifacts from the
-threading subsystem of the parent process. For example, a mutex may inherit
-a wait queue of threads waiting for the lock; this wait queue makes no sense
-in the child process. Initializing the mutex takes care of this.
-
-@node Streams and Fork
-@section Streams and Fork
-
-The GNU standard I/O library has an internal mutex which guards the internal
-linked list of all standard C FILE objects. This mutex is properly taken care
-of during @code{fork} so that the child receives an intact copy of the list.
-This allows the @code{fopen} function, and related stream-creating functions,
-to work correctly in the child process, since these functions need to insert
-into the list.
-
-However, the individual stream locks are not completely taken care of. Thus
-unless the multithreaded application takes special precautions in its use of
-@code{fork}, the child process might not be able to safely use the streams that
-it inherited from the parent. In general, for any given open stream in the
-parent that is to be used by the child process, the application must ensure
-that that stream is not in use by another thread when @code{fork} is called.
-Otherwise an inconsistent copy of the stream object be produced. An easy way to
-ensure this is to use @code{flockfile} to lock the stream prior to calling
-@code{fork} and then unlock it with @code{funlockfile} inside the parent
-process, provided that the parent's threads properly honor these locks.
-Nothing special needs to be done in the child process, since the library
-internally resets all stream locks.
-
-Note that the stream locks are not shared between the parent and child.
-For example, even if you ensure that, say, the stream @code{stdout} is properly
-treated and can be safely used in the child, the stream locks do not provide
-an exclusion mechanism between the parent and child. If both processes write
-to @code{stdout}, strangely interleaved output may result regardless of
-the explicit use of @code{flockfile} or implicit locks.
-
-Also note that these provisions are a GNU extension; other systems might not
-provide any way for streams to be used in the child of a multithreaded process.
-POSIX requires that such a child process confines itself to calling only
-asynchronous safe functions, which excludes much of the library, including
-standard I/O.
-
-@node Miscellaneous Thread Functions
-@section Miscellaneous Thread Functions
-
-@comment pthread.h
-@comment POSIX
-@deftypefun {pthread_t} pthread_self (@var{void})
-@code{pthread_self} returns the thread identifier for the calling thread.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_equal (pthread_t thread1, pthread_t thread2)
-@code{pthread_equal} determines if two thread identifiers refer to the same
-thread.
-
-A non-zero value is returned if @var{thread1} and @var{thread2} refer to
-the same thread. Otherwise, 0 is returned.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_detach (pthread_t @var{th})
-@code{pthread_detach} puts the thread @var{th} in the detached
-state. This guarantees that the memory resources consumed by @var{th}
-will be freed immediately when @var{th} terminates. However, this
-prevents other threads from synchronizing on the termination of @var{th}
-using @code{pthread_join}.
-
-A thread can be created initially in the detached state, using the
-@code{detachstate} attribute to @code{pthread_create}. In contrast,
-@code{pthread_detach} applies to threads created in the joinable state,
-and which need to be put in the detached state later.
-
-After @code{pthread_detach} completes, subsequent attempts to perform
-@code{pthread_join} on @var{th} will fail. If another thread is already
-joining the thread @var{th} at the time @code{pthread_detach} is called,
-@code{pthread_detach} does nothing and leaves @var{th} in the joinable
-state.
-
-On success, 0 is returned. On error, one of the following codes is
-returned:
-@table @code
-@item ESRCH
-No thread could be found corresponding to that specified by @var{th}
-@item EINVAL
-The thread @var{th} is already in the detached state
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment GNU
-@deftypefun void pthread_kill_other_threads_np (@var{void})
-@code{pthread_kill_other_threads_np} is a non-portable LinuxThreads extension.
-It causes all threads in the program to terminate immediately, except
-the calling thread which proceeds normally. It is intended to be
-called just before a thread calls one of the @code{exec} functions,
-e.g. @code{execve}.
-
-Termination of the other threads is not performed through
-@code{pthread_cancel} and completely bypasses the cancellation
-mechanism. Hence, the current settings for cancellation state and
-cancellation type are ignored, and the cleanup handlers are not
-executed in the terminated threads.
-
-According to POSIX 1003.1c, a successful @code{exec*} in one of the
-threads should automatically terminate all other threads in the program.
-This behavior is not yet implemented in LinuxThreads. Calling
-@code{pthread_kill_other_threads_np} before @code{exec*} achieves much
-of the same behavior, except that if @code{exec*} ultimately fails, then
-all other threads are already killed.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_once (pthread_once_t *once_@var{control}, void (*@var{init_routine}) (void))
-
-The purpose of @code{pthread_once} is to ensure that a piece of
-initialization code is executed at most once. The @var{once_control}
-argument points to a static or extern variable statically initialized
-to @code{PTHREAD_ONCE_INIT}.
-
-The first time @code{pthread_once} is called with a given
-@var{once_control} argument, it calls @var{init_routine} with no
-argument and changes the value of the @var{once_control} variable to
-record that initialization has been performed. Subsequent calls to
-@code{pthread_once} with the same @code{once_control} argument do
-nothing.
-
-If a thread is cancelled while executing @var{init_routine}
-the state of the @var{once_control} variable is reset so that
-a future call to @code{pthread_once} will call the routine again.
-
-If the process forks while one or more threads are executing
-@code{pthread_once} initialization routines, the states of their respective
-@var{once_control} variables will appear to be reset in the child process so
-that if the child calls @code{pthread_once}, the routines will be executed.
-
-@code{pthread_once} always returns 0.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setschedparam (pthread_t target_@var{thread}, int @var{policy}, const struct sched_param *@var{param})
-
-@code{pthread_setschedparam} sets the scheduling parameters for the
-thread @var{target_thread} as indicated by @var{policy} and
-@var{param}. @var{policy} can be either @code{SCHED_OTHER} (regular,
-non-realtime scheduling), @code{SCHED_RR} (realtime, round-robin) or
-@code{SCHED_FIFO} (realtime, first-in first-out). @var{param} specifies
-the scheduling priority for the two realtime policies. See
-@code{sched_setpolicy} for more information on scheduling policies.
-
-The realtime scheduling policies @code{SCHED_RR} and @code{SCHED_FIFO}
-are available only to processes with superuser privileges.
-
-On success, @code{pthread_setschedparam} returns 0. On error it returns
-one of the following codes:
-@table @code
-@item EINVAL
-@var{policy} is not one of @code{SCHED_OTHER}, @code{SCHED_RR},
-@code{SCHED_FIFO}, or the priority value specified by @var{param} is not
-valid for the specified policy
-
-@item EPERM
-Realtime scheduling was requested but the calling process does not have
-sufficient privileges.
-
-@item ESRCH
-The @var{target_thread} is invalid or has already terminated
-
-@item EFAULT
-@var{param} points outside the process memory space
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_getschedparam (pthread_t target_@var{thread}, int *@var{policy}, struct sched_param *@var{param})
-
-@code{pthread_getschedparam} retrieves the scheduling policy and
-scheduling parameters for the thread @var{target_thread} and stores them
-in the locations pointed to by @var{policy} and @var{param},
-respectively.
-
-@code{pthread_getschedparam} returns 0 on success, or one of the
-following error codes on failure:
-@table @code
-@item ESRCH
-The @var{target_thread} is invalid or has already terminated.
-
-@item EFAULT
-@var{policy} or @var{param} point outside the process memory space.
-
-@end table
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_setconcurrency (int @var{level})
-@code{pthread_setconcurrency} is unused in LinuxThreads due to the lack
-of a mapping of user threads to kernel threads. It exists for source
-compatibility. It does store the value @var{level} so that it can be
-returned by a subsequent call to @code{pthread_getconcurrency}. It takes
-no other action however.
-@end deftypefun
-
-@comment pthread.h
-@comment POSIX
-@deftypefun int pthread_getconcurrency ()
-@code{pthread_getconcurrency} is unused in LinuxThreads due to the lack
-of a mapping of user threads to kernel threads. It exists for source
-compatibility. However, it will return the value that was set by the
-last call to @code{pthread_setconcurrency}.
-@end deftypefun
Modified: glibc-doc-reference/trunk/manual/locale.texi
===================================================================
--- glibc-doc-reference/trunk/manual/locale.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/locale.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1210,7 +1210,7 @@
/* @r{Prepare the @code{getline} call.} */
line = NULL;
len = 0;
- while (getline (&line, &len, stdout) >= 0)
+ while (getline (&line, &len, stdin) >= 0)
@{
/* @r{Check the response.} */
int res = rpmatch (line);
Modified: glibc-doc-reference/trunk/manual/math.texi
===================================================================
--- glibc-doc-reference/trunk/manual/math.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/math.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1421,7 +1421,7 @@
The GNU C library contains four additional functions which contain the
state as an explicit parameter and therefore make it possible to handle
-thread-local PRNGs. Beside this there are no difference. In fact, the
+thread-local PRNGs. Beside this there is no difference. In fact, the
four functions already discussed are implemented internally using the
following interfaces.
Modified: glibc-doc-reference/trunk/manual/memory.texi
===================================================================
--- glibc-doc-reference/trunk/manual/memory.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/memory.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -702,6 +702,11 @@
@item M_MMAP_MAX
The maximum number of chunks to allocate with @code{mmap}. Setting this
to zero disables all use of @code{mmap}.
+@item M_PERTURB
+If non-zero, memory blocks are filled with values depending on some
+low order bits of this parameter when they are allocated (except when
+allocated by @code{calloc}) and freed. This can be used to debug the
+use of uninitialized or freed heap memory.
@end table
@end deftypefun
@@ -2379,7 +2384,7 @@
@c The Brk system call in Linux (as opposed to the GNU C Library function)
@c is considerably different. It always returns the new end of the data
@c segment, whether it succeeds or fails. The GNU C library Brk determines
-@c it's a failure if and only if if the system call returns an address less
+@c it's a failure if and only if the system call returns an address less
@c than the address requested.
@end deftypefun
Modified: glibc-doc-reference/trunk/manual/message.texi
===================================================================
--- glibc-doc-reference/trunk/manual/message.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/message.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1466,7 +1466,7 @@
handle these kind of problems with the @code{gettext} functions.
@noindent
-As as example consider the following fictional situation. A GUI program
+As an example consider the following fictional situation. A GUI program
has a menu bar with the following entries:
@smallexample
Modified: glibc-doc-reference/trunk/manual/resource.texi
===================================================================
--- glibc-doc-reference/trunk/manual/resource.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/resource.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -1288,7 +1288,7 @@
The POSIX standard up to this date is of not much help to solve this
problem. The Linux kernel provides a set of interfaces to allow
specifying @emph{affinity sets} for a process. The scheduler will
-schedule the thread or process on on CPUs specified by the affinity
+schedule the thread or process on CPUs specified by the affinity
masks. The interfaces which the GNU C library define follow to some
extend the Linux kernel interface.
Modified: glibc-doc-reference/trunk/manual/stdio.texi
===================================================================
--- glibc-doc-reference/trunk/manual/stdio.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/stdio.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -574,7 +574,7 @@
introduction of threads) were implemented as macros which are very fast
if the buffer is not empty. With the addition of locking requirements
these functions are no longer implemented as macros since they would
-would expand to too much code.
+expand to too much code.
But these macros are still available with the same functionality under the new
names @code{putc_unlocked} and @code{getc_unlocked}. This possibly huge
difference of speed also suggests the use of the @code{_unlocked}
Added: glibc-doc-reference/trunk/manual/texis
===================================================================
--- glibc-doc-reference/trunk/manual/texis (rev 0)
+++ glibc-doc-reference/trunk/manual/texis 2011-05-02 18:20:00 UTC (rev 4639)
@@ -0,0 +1,89 @@
+texis = \
+intro.texi \
+creature.texi \
+errno.texi \
+memory.texi \
+ctype.texi \
+string.texi \
+stpcpy.c.texi \
+strdupa.c.texi \
+strncat.c.texi \
+charset.texi \
+locale.texi \
+message.texi \
+search.texi \
+search.c.texi \
+pattern.texi \
+io.texi \
+stdio.texi \
+rprintf.c.texi \
+memopen.c.texi \
+memstrm.c.texi \
+fmtmsgexpl.c.texi \
+llio.texi \
+select.c.texi \
+filesys.texi \
+dir.c.texi \
+dir2.c.texi \
+pipe.texi \
+pipe.c.texi \
+popen.c.texi \
+socket.texi \
+mkfsock.c.texi \
+mkisock.c.texi \
+isockad.c.texi \
+inetcli.c.texi \
+inetsrv.c.texi \
+filesrv.c.texi \
+filecli.c.texi \
+terminal.texi \
+termios.c.texi \
+syslog.texi \
+math.texi \
+libm-err.texi \
+arith.texi \
+time.texi \
+strftim.c.texi \
+resource.texi \
+setjmp.texi \
+setjmp.c.texi \
+swapcontext.c.texi \
+signal.texi \
+sigh1.c.texi \
+sigusr.c.texi \
+startup.texi \
+getopt.texi \
+testopt.c.texi \
+longopt.c.texi \
+argp.texi \
+argp-ex1.c.texi \
+argp-ex2.c.texi \
+argp-ex3.c.texi \
+argp-ex4.c.texi \
+subopt.c.texi \
+atexit.c.texi \
+process.texi \
+job.texi \
+nss.texi \
+nsswitch.texi \
+users.texi \
+db.c.texi \
+sysinfo.texi \
+conf.texi \
+crypt.texi \
+mygetpass.c.texi \
+genpass.c.texi \
+testpass.c.texi \
+debug.texi \
+execinfo.c.texi \
+lang.texi \
+add.c.texi \
+header.texi \
+summary.texi \
+install.texi \
+maint.texi \
+contrib.texi \
+freemanuals.texi \
+lesser.texi \
+fdl.texi \
+
Modified: glibc-doc-reference/trunk/manual/time.texi
===================================================================
--- glibc-doc-reference/trunk/manual/time.texi 2011-05-02 18:17:39 UTC (rev 4638)
+++ glibc-doc-reference/trunk/manual/time.texi 2011-05-02 18:20:00 UTC (rev 4639)
@@ -972,7 +972,7 @@
large offsets or jitter).
@item long int stbcnt
-This counter denotes the number of of calibrations where the stability
+This counter denotes the number of calibrations where the stability
exceeded the threshold.
@end table
@end deftp
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