Bug#121642: libstdc++3: Unable to do buffered cout (?)
Package: libstdc++3
Version: 1:3.0.2-3
Severity: normal
Hi!
I have seen an strange behaviour of libstdc++ regarding buffering of
streams; I don't know if it is my fault or the libraries fault. It
basically writes character per character whenever I do a cout <<
"something".
Given the following program:
#include <iostream>
using namespace std;
int main (void)
{
cout << "Hello world!" << endl;
return 0;
}
compiled it with gcc-2.95 and gcc-3.0 (ok, g++ actually). When
compiled with gcc-2.95 and run with strace(1), I get the following:
$ g++-2.95 -Wall -O2 testout.cc -o testout
$ ./testout
Hello world!
$ strace ./testout > /dev/null
execve("./testout", ["./testout"], [/* 28 vars */]) = 0
uname({sys="Linux", node="milikk", ...}) = 0
brk(0) = 0x8049834
open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=66967, ...}) = 0
old_mmap(NULL, 66967, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40016000
close(3) = 0
open("/usr/lib/libstdc++-libc6.2-2.so.3", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`\251\1"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0644, st_size=291720, ...}) = 0
old_mmap(NULL, 303748, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x40027000
mprotect(0x4005e000, 78468, PROT_NONE) = 0
old_mmap(0x4005e000, 69632, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x36000) = 0x4005e000
old_mmap(0x4006f000, 8836, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4006f000
close(3) = 0
open("/lib/libm.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 I\0\000"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0644, st_size=134668, ...}) = 0
old_mmap(NULL, 137220, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x40072000
mprotect(0x40093000, 2052, PROT_NONE) = 0
old_mmap(0x40093000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x20000) = 0x40093000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0(\327\1"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0755, st_size=1171196, ...}) = 0
old_mmap(NULL, 1187968, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x40094000
mprotect(0x401ac000, 41088, PROT_NONE) = 0
old_mmap(0x401ac000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x117000) = 0x401ac000
old_mmap(0x401b2000, 16512, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401b2000
close(3) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x401b7000
munmap(0x40016000, 66967) = 0
fstat64(1, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 3), ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE, 0xbffff718) = -1 ENOTTY (Inappropriate ioctl for device)
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40016000
write(1, "Hello world!\n", 13) = 13
_exit(0) = ?
Note the previous-to-last line, write(1, "Hello world!\n", 13), that
is, a buffered write, as expected. However, now let's do the same with
3.0:
$ g++-3.0 -Wall -O2 testout.cc -o testout
$ ./testout
Hello world!
$ strace ./testout > /dev/null
execve("./testout", ["./testout"], [/* 28 vars */]) = 0
uname({sys="Linux", node="milikk", ...}) = 0
brk(0) = 0x804c890
open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=66967, ...}) = 0
old_mmap(NULL, 66967, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40016000
close(3) = 0
open("/usr/lib/libstdc++.so.3", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260\255"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0644, st_size=565536, ...}) = 0
old_mmap(NULL, 587464, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x40027000
mprotect(0x4009e000, 100040, PROT_NONE) = 0
old_mmap(0x4009e000, 81920, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x76000) = 0x4009e000
old_mmap(0x400b2000, 18120, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x400b2000
close(3) = 0
open("/lib/libm.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 I\0\000"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0644, st_size=134668, ...}) = 0
old_mmap(NULL, 137220, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x400b7000
mprotect(0x400d8000, 2052, PROT_NONE) = 0
old_mmap(0x400d8000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x20000) = 0x400d8000
close(3) = 0
open("/lib/libgcc_s.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\330\22"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0644, st_size=27180, ...}) = 0
old_mmap(NULL, 30220, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x400d9000
mprotect(0x400df000, 5644, PROT_NONE) = 0
old_mmap(0x400df000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x5000) = 0x400df000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0(\327\1"..., 1024) = 1024
fstat64(3, {st_mode=S_IFREG|0755, st_size=1171196, ...}) = 0
old_mmap(NULL, 1187968, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x400e1000
mprotect(0x401f9000, 41088, PROT_NONE) = 0
old_mmap(0x401f9000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x117000) = 0x401f9000
old_mmap(0x401ff000, 16512, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401ff000
close(3) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40204000
munmap(0x40016000, 66967) = 0
brk(0) = 0x804c890
brk(0x804c8c8) = 0x804c8c8
brk(0x804d000) = 0x804d000
brk(0x804e000) = 0x804e000
fstat64(1, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 3), ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE, 0xbffff654) = -1 ENOTTY (Inappropriate ioctl for device)
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40016000
write(1, "H", 1) = 1
write(1, "e", 1) = 1
write(1, "l", 1) = 1
write(1, "l", 1) = 1
write(1, "o", 1) = 1
write(1, " ", 1) = 1
write(1, "w", 1) = 1
write(1, "o", 1) = 1
write(1, "r", 1) = 1
write(1, "l", 1) = 1
write(1, "d", 1) = 1
write(1, "!", 1) = 1
write(1, "\n", 1) = 1
munmap(0x40016000, 4096) = 0
_exit(0) = ?
And puf! there you have it, unbuffered, one char at a time, super
innefective writes.
I tried to investigate and found nothing. I was thinking maybe
there is a switch for it or something, but found none. Anyway, by
default, the output should be buffered, AFAIK ... and unless I am
missing anything.
Any clues?
Thanks!!!
-- System Information
Debian Release: testing/unstable
Kernel Version: Linux milikk 2.4.10.2-milikk #1 SMP mar oct 30 15:30:23 PST 2001 i686 unknown
Versions of the packages libstdc++3 depends on:
ii gcc-3.0-base 3.0.2-3 The GNU Compiler Collection (base package).
ii libc6 2.2.4-6 GNU C Library: Shared libraries and Timezone
ii libgcc1 3.0.2-3 GCC support library.
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