[libdispatch-dev] autoconf HAVE macro conventions
Robert Watson
robert at fledge.watson.org
Sat Oct 31 03:00:18 PDT 2009
On Fri, 30 Oct 2009, Kevin Van Vechten wrote:
> I'm not very familiar with autoconf conventions and was wondering why some
> config.h values are merely defined and some are explicitly defined to 1.
>
> Is there a strong convention to do #ifdef HAVE_FOO instead of #if HAVE_FOO
> when testing for configure features? For various reasons, the ability to
> define a macro to 0 or 1 would be useful for the Mac OS X version of
> config.h — it would let us define certain features in terms of other
> features without as much conditional logic.
As I understand it, some of this is simply a feature of the way autoconf
works: AC_CHECK_DECLS(), used for testing macros, checks conditionally define
HAVE_DECL_foo, whereas functional checks, such as AC_CHECK_FUNCS(), used for
testing for functions, defines HAVE_foo unconditionally but with a value of 0
or 1. I'd be quite happy to learn about ways to avoid this happening. :-)
Robert N M Watson
Computer Laboratory
University of Cambridge
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