Re: Bug#126703: g++-3.0: <stdio.h> defines _GNU_SOURCE with g++-3.0
On Mon, Dec 31, 2001 at 01:38:06AM +0100, Matthias Klose wrote:
> Martin v. Loewis writes:
> > > > I can't see a reason for libstdc++ requiring _GNU_SOURCE except for the
> > > > desire to re-export symbols in std::, for which I would propose a
> > > > different strategy.
> > >
> > > It would help to know why this was done in the first place; there could be
> > > other reasons.
Mail archives are our friends. :-) See below.
> [short question ... is this forum appropriate for this discussion or
> should we CC libstdc++@gcc.gnu.org?]
If you have questions (or better yet, patches *grin*), by all means include
the list. However, if you do, I'd recommend /not/ cc'ing @bugs.debian.org,
because those auto-acks are awfully annoying.
Here's a super-short summary of _GNU_SOURCE. (Now, I am not the expert on
this, so if you have more questions, /please/ contact the lists.) We need
the symbol to be defined before including any header which could possibly
include a glibc header, otherwise certain C++ programs will simply fail
out of the box. The C++ rules are much stricter than in C (duh), and in
order to get standard-conforming semantics out of glibc 2.2, we had to
feed it _GNU_SOURCE. (Making glibc happier with C++ is a goal for 2.3,
I'm told. Making libstdc++-v3 not require _GNU_SOURCE in the first place
is also a goal.)
The change was initially made here:
http://gcc.gnu.org/ml/libstdc++/2000-12/msg00215.html
and there's an example of code which needs to not break.
Time passed.
Somebody moved the _GNU_SOURCE definition into the compiler itself, for
all platforms. Somebody else noticed and complained here:
http://gcc.gnu.org/ml/gcc/2001-06/msg00108.html
which started a huge thread, all instructive. The end result was that
_GNU_SOURCE is defined by the compiler, only in C++ mode, only for those
platforms which use glibc, because otherwise code such as the example in
the first message Just Won't Work.
(This series of changes allowed us to make --enable-long-long the default
again.)
Yes, it's a mess for glibc-using platforms. Solutions welcome. :-)
Phil
--
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