Re: AC_PROG_CC_STDC

[Peter Eisentraut]

Paul Eggert writes:

> > I've been thinking lately about the issues surrounding this macro (see
> > archives and TODO list).  Is there any reason why AC_PROG_CC_STDC could
> > not simply be folded into AC_PROG_CC?  Is there any software that must
> > avoid an ANSI C compiler at all cost?

> In the past I recall some problems with that macro, as it set options
> that caused some compilers to become pedantic (e.g., to refuse to
> define `fileno' in <stdio.h>, since the C standard does not allow
> that).

I can see that.  The problem is that the macro tests the flags

# AIX                   -qlanglvl=ansi
# Ultrix and OSF/1      -std1
# HP-UX 10.20 and later -Ae
# HP-UX older versions  -Aa -D_HPUX_SOURCE
# SVR4                  -Xc -D__EXTENSIONS__

where -qlanglvl=ansi and -std1 select the "strict" ANSI mode, whereas one
could use -qlanglvl=extended and -std to get the "relaxed" ANSI mode.
However, both of these options are the default in newer compilers, so this
code doesn't get exercised anymore.  The only compiler I know of that
needs a flag to grok ANSI code at all is HP-UX's.

> A reasonable amount of GNU code still tries to be portable to K&R C.
> GNU Emacs comes to mind.  However, hardly anybody actually uses K&R C
> compilers anymore, except perhaps the GCC folks while bootstrapping.
> So the K&R mode doesn't get tested much these days.

Code that tries to be portable to K&R uses some restricted subset of C
that is portable both ways, so it wouldn't break if we ran it through an
ANSI C compiler.

There is, I claim, no code that we would have to be concerned about that,
requires K&R semantics only.  Such code wouldn't work with Autoconf
anyway, because configure would pick up 'gcc' and that doesn't provide
strict K&R semantics.

If you're concerned about this, let's provide some sort of extra switch or
argument to prevent AC_PROG_CC from setting ANSI C mode.  But I think the
default should be to provide a compiler setup that works for today's code.

-- 
Peter Eisentraut   address@hidden