Re: AC_CHECK_SIZEOF failing on undefined HAVE_STDINT_H with -Werror

[Ralf Wildenhues]

* David Fang wrote on Wed, Aug 16, 2006 at 02:15:09AM CEST:
> > Thanks for reporting this; I didn't realize it was a regression.
> > -Wundef is a bit controversial, but it's easy for Autoconf to support
> > its use for programmers that prefer it, so I installed the following
> > patch.

> In practice, I have actually caught one or two serious errors using
> -Wundef -Werror, as anal-retentive and controversial as it may seem.
> YMMV.

In practice, with the set of warning flags you posted previously, you
will break several Autoconf macros in very subtle ways (and no, not all
are easy to fix).

> Wasn't it pointed out in this thread (#if vs. #ifdef) that evaluating
> an undefined macro with #if is undefined in standard C?  (i.e. cannot
> assumed to be equivalent to evaluating 0).

It was claimed but then proved to be a false statement.  IOW: evaluating
an undefined macro with #if is perfectly acceptable C89.

> Also perhaps it should be noted somewhere that while autoconf's m4 macros
> now use #ifdef to conditionally include headers, users may still use
> #if USER_DEFINED_MACRO as long as the said macro is defined in all cases
> by the configure test.  This internal change doesn't force any users to
> define and use configure macros with one convention or the other.  The
> important thing is that definition and use are consistent.

Not with the direction the change is going now.  Au contraire: it is
safe for users to use #if throughout; their motivation to change would
stem from the desire to be able to build with '-Wundef -Werror', not any
change within Autoconf.

> Just confirming: will this revision appear in release 2.61?

Unless it is reverted in some way, yes.

Cheers,
Ralf