CODEWITHSUNDEEP
cautotoolsautoconf
pevik
pevik

Reputation: 4801

Check value of C #define with autoconf

I know I can use AC_CHECK_DECL / AC_CHECK_DECLS to check whether a set of headers provides a declaration for a specified identifier, but how can I check not only whether a macro is declared, but also whether its expansion meets my criteria? Specifically, I would like to check whether numa.h contains a macro definition equivalent to this ...

#define LIBNUMA_API_VERSION 2

... including the specific value "2".

UPDATE: <numa.h> header contains a definition such as #define LIBNUMA_API_VERSION 2 to declare it's version. C code that uses this header typically uses it like so:

#if defined(LIBNUMA_API_VERSION) && LIBNUMA_API_VERSION >= 2
....
#endif

I want to determine NUMA header version with autoconf, and define a macro that succinctly conveys whether NUMA version 2 is provided. i.e.:

if test "$have_numa_v2" = "yes" ; then
    AC_DEFINE(NUMA_VERSION_2, 1, [Determine whether NUMA v2 available)
fi

That could be used like so:

#ifdef NUMA_VERSION_2
....
#endif

Is it possible? I'm having trouble determining how I could set the value of variable have_numa_v2 variable in my Autoconf file.

Upvotes: 1

Views: 1853

Answers (1)

John Bollinger
John Bollinger

Reputation: 180201

You can use AC_COMPILE_IFELSE or AC_RUN_IFELSE with a suitably-structured test program to determine whether the macro is defined to a specific value you designate. For example, supposing that the current language is C:

have_numa_v2=no
AC_RUN_IFELSE([AC_LANG_PROGRAM([
#include <numa.h>
],[
#if LIBNUMA_API_VERSION != 2
exit(1);
#endif
])], [have_numa_v2=yes])

That constructs a program whose return value depends on whether LIBNUMA_API_VERSION is defined as a macro, and if so, whether it expands to 2. If Autoconf cannot compile it (because, say, it cannot find numa.h) or if it exits with a status other than 0 then nothing else happens ($have_numa_v2 retains its assigned value of "no"). Otherwise, the assignment in the second argument is performed, and $have_numa_v2 ends up with the value "yes".

For what it's worth, the source of the particular test program produced and used by that macro contains some Autoconf-standard macro definitions, plus this:

#include <numa.h>

int
main ()
{

#if LIBNUMA_API_VERSION != 2
exit(1);
#endif

  ;
  return 0;
}

The version using AC_COMPILE_IFELSE would be similar, but built around using an #error preprocessor directive to make compilation fail if the macro is not defined to the specified value. That variation might be a better choice if you anticipate any possibility that your program will be cross-compiled for a foreign architecture.

Upvotes: 6

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