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Re: AC_CHECK_FUNCS(sigsetjmp)

From: Eric Blake
Subject: Re: AC_CHECK_FUNCS(sigsetjmp)
Date: Sat, 29 Jul 2006 17:43:20 +0000

> The real problem that I was trying to illuminate is that the fact that 
> if a particular
> interface was implemented as a macro then the AC_CHECK_FUNCS() breaks.

Most POSIX functions are required to exist as a linkable function, even
if they are also implemented as a macro.  There are relatively few
exceptions on this front.

> Some seem to argue that one should always know if a particular interface 
> might
> be implemented as a macro (or compiler internal?). If so, then you have to
> roll your own autoconf macro. My point is that it would be more user 
> friendly
> if AC_CHECK_FUNCS (or a newly named AC macro) were to presume that if
> either you could link to the external name or if the external name were 
> #define-d,
> then you #define HAVE_INTERFACE.

It already exists - AC_CHECK_DECLS.

And for the weirdest of cases, the combination of AC_CHECK_DECLS
with AC_CHECK_FUNCS gives you the full check support for all four
possible cases:

declared and working
mistakenly declared but not implemented
linkable but undeclared
completely missing

Eric Blake

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