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Re: No macro for C11/C18?

From: Andrew W. Nosenko
Subject: Re: No macro for C11/C18?
Date: Fri, 7 Feb 2020 00:15:07 +0200

On Wed, Feb 5, 2020 at 5:56 PM Nick Bowler <address@hidden> wrote:

> On 2020-02-01, Andrew W. Nosenko <address@hidden> wrote:
> > On Fri, Jan 24, 2020 at 9:48 PM Nick Bowler <address@hidden> wrote:
> > > AC_PROG_CC now tries to select the highest language revision supported
> > > by the compiler.
> >
> > These macros (AC_PROG_CC_C99 vs. new AC_PROG_CC) have different
> > semantics.  AC_PROG_CC_C99 — select best/prefered compiler that
> > supports particular standard (c99), while new AC_PROG_CC — select
> > best/most recent standard supported by particular compiler.
> >
> > So deprecating one in favour of another is quite like deprecating
> > apples in favour of oranges.
> I think you are misunderstanding what AC_PROG_CC_C99 actually does.
> It does not search for a compiler that supports C99.  It picks the
> first compiler it finds in a list (or uses the compiler specified by
> the user via CC), and then checks whether one of several options
> are needed to enable support for C99.  This macro is best effort:
> if the compiler it found only supports C89 then you get a C89 compiler,
> or if the compiler supports C11 by default then you get a C11 compiler.
> It is *exactly* the same as the new AC_PROG_CC, except that now these
> macros will first try to find options that enable C11 before looking
> for options that enable C99.  In practice there are probably not a
> lot of compilers where this makes any difference at all (quite possibly
> just gcc-4.7 through gcc-4.9 and maybe some very early versions of clang).
> A C11 compiler can compile C99 code so there should be no portability
> problem if a C11 compiler is selected for a package that requires C99
> features.

I wonder not about obtaining c11 mode instead of c99.  I wonder to obtain
c89.  Under AC_PROG_CC_C99 I can check ac_cv_prog_cc_c99.  But what to
check under floating AC_PROG_CC?  (Current AC_PROG_CC_STDC has similar
semantics — tries to set highest possible standard.  And useless.  Because
says only one thing: yes, some compiler found, and it supports some
(unspecified) standard).

Andrew W. Nosenko <address@hidden>

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