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From: Paul Eggert
Subject: Re: AC_PROG_CC_C99
Date: Thu, 02 Dec 2004 10:50:19 -0800
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux)

Ralf Wildenhues <address@hidden> writes:

> This worries me to some extent.  While C99 is mostly backwards
> compatible with C89, it has removed some deprecated things such as
>   functions return implicit int,
>   implicit function declaration.

In practice this shouldn't be much of a problem, since C99 compilers
(in extended mode, which is what we want) will allow these features
for obvious backwards-compatibility reasons.  We may have a problem
where a compiler is put into pedantic mode by mistake.  But this will
be a bug, that we should fix, and in the meantime users can work
around the problem by setting CC in their environment.

I only know of one true C99 compiler, by the way -- the Edison front
end -- and I've never used it.  It's not free, unfortunately.  It'd be
nice if someone with access to that compiler could test all this

> it will silently break Autoconf macros which use implicitly declared
> functions, e.g. within deprecated AC_TRY_RUN constructs.

Such macros would already already be broken for pedantic C99
implementations, and we ought to fix them.  However, I don't
think defaulting to C99 will make the problem much worse, for
reasons discussed above.

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