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Re: AC_PROG_CC_C99 macro description is too vague / ambiguous

From: Eric Blake
Subject: Re: AC_PROG_CC_C99 macro description is too vague / ambiguous
Date: Tue, 14 Apr 2009 06:48:44 -0600
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According to Vincent Lefevre on 3/24/2009 5:39 PM:
> Hi,

Hello Vincent, and sorry for the delayed reply,

> The documentation of AC_PROG_CC_C99 is rather vague:
> It is not clear whether GNU extensions are allowed or not. Even though
> one may think that it is natural to keep the GNU extensions, gcc has
> -std=c99 for strict ISO C99 (as opposed to gnu99 for the GNU dialect),
> so that one can easily mix up "C99 mode" above and "c99 language" from
> gcc. The macro description should avoid this possible confusion.

I agree that we could polish up the wording, but don't know how best to
word it.  If you can provide some sentences that would make more sense to
you, I would be happy to polish it into a proper patch.

The intent is that AC_PROG_CC_C99 puts the compiler into whatever mode
accepts the largest amount of C99 constructs (since very few, if any,
compiler is fully C99 compliant yet), while possibly enabling other
compiler extensions.  The mere use of AC_PROG_CC_C99 does not guarantee
that particular GNU extensions not required by C99 will be available, but
the intent is that it does not preclude them either.  You will have to
perform a separate test to see whether a particular GNU extension is
supported by the current compiler.  At any rate, I think that
AC_PROG_CC_C99 should be targetting --std=gnu99 and not --std=c99.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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