Re: Gnulib needed in AC_CHECK_HEADERS

[Bruno Haible]

Sylvain Beucler wrote:
> I'm cross-compiling an SDL application for i586-mingw32mscv.  I
> imported the alloca module from Gnulib, as a dependency of strcasestr.

You mean the 'alloca-opt' module, I guess?

> When checking for SDL.h,
> 
>   AC_CHECK_HEADERS(SDL.h SDL_rotozoom.h SDL_framerate.h SDL_image.h,
>     [], AC_MSG_ERROR([Could not find necessary SDL libs headers]))
> 
> ../configure fails checking for SDL.h, because SDL.h (more exactly
> SDL_stdinc.h), seeing HAVE_ALLOCA set, tries to include <alloca.h>,
> and fails (mingw doesn't have alloca.h).

SDL-1.2.10/include/SDL_stdinc.h has

#if defined(HAVE_ALLOCA) && !defined(alloca)
# if defined(HAVE_ALLOCA_H)
#  include <alloca.h>
# elif defined(__GNUC__)
#  define alloca __builtin_alloca
# elif defined(_MSC_VER)
#  include <malloc.h>
#  define alloca _alloca
# elif defined(__WATCOMC__)
#  include <malloc.h>
# elif defined(__AIX__)
  #pragma alloca
# elif defined(__MRC__)
   void *alloca (unsigned);
# else
   char *alloca ();
# endif
#endif

So I think you mean HAVE_ALLOCA_H.

> How would you deal with this?

Indeed gnulib defines HAVE_ALLOCA_H always:

   2004-05-16  Paul Eggert  <address@hidden>

        * m4/alloca.m4 (gl_FUNC_ALLOCA): Define HAVE_ALLOCA_H always,
        for backward compatibility with older code.

I think this is right. There are so many places in code which test
HAVE_ALLOCA_H.

SDL_stdinc.h is also right: It can be used without or with gnulib.
It would be very ugly if it #included different files at configure time
than later, at build time.

Therefore I agree with you that adding some temporary -I options to
CPPFLAGS while testing for SDL.h is the best workaround.

Bruno