Re: CFLAGS for AC_COMPILE_IFELSE.

[Edward Tomasz Napierala]

On 0512T0631, Ralf Corsepius wrote:
> > I need the configure script to figure out how many parameters one particular
> > library function requires, due to API change.  I've found a macro to do 
> > that,
> > it looks like this:
> > 
> > AC_DEFUN([AC_JACK_MIDI_NFRAMES_CHECK], [
> > AC_MSG_CHECKING([whether JACK MIDI functions need nframes parameter])
> > AC_LANG_PUSH(C)
> > AC_COMPILE_IFELSE(AC_LANG_PROGRAM([[
> > #include <jack/jack.h>
> > #include <jack/midiport.h>
> > ]], [[
> > jack_midi_event_get(0, 0, 0, 0);
> > ]]), [jackmidi_nframes='yes'], [jackmidi_nframes='no'])
> > AC_MSG_RESULT([$jackmidi_nframes])
> > AC_LANG_POP()
> > ])
> > 
> > Problem is, it does not work for me.  Probable reason is this
> > (from config.log):
> > 
> > configure:5138: checking whether JACK MIDI functions need nframes parameter
> > configure:5172: gcc -c -g -O2  conftest.c >&5
> > conftest.c:32:23: error: jack/jack.h: No such file or directory
> > conftest.c:33:27: error: jack/midiport.h: No such file or directory
> > 
> > It does not work, because it does not use the proper CFLAGS - this
> > is FreeBSD, includes live in /usr/local/include and it's neccessary
> > to pass -I/usr/local/include.
> Are you saying, they modified their GCC in such a way that it doesn't
> look into /usr/local/include?

Yes, it seems so.

> GCC's default behavior is to
> use /usr/local/include implicitly, as part of GCC's system-include path,
> in a similar way it treats /usr/include.

What about systems that put external libraries somewhere under
/opt or /usr/pkg?

> > So, the question is, how to modify the above macro to use CFLAGS it got
> > (or should got) from pkg-config, for example?
> You should not do this. Instead, the user/installer is supposed to pass
> appropriate *FLAGS to configure.
>
> In your case (include-paths): ..../configure CPPFLAGS="-I<foo>/include"

I see.  Anyway, I managed to work around that problem by checking for
the particular version of library using PKG_CHECK_MODULES.  Thanks ;-)

-- 
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