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Re: documentation of AC_FUNC_ALLOCA and mingw-w64 compilers

From: Bob Friesenhahn
Subject: Re: documentation of AC_FUNC_ALLOCA and mingw-w64 compilers
Date: Sun, 22 Jan 2012 09:21:35 -0600 (CST)
User-agent: Alpine 2.01 (GSO 1266 2009-07-14)

On Sun, 22 Jan 2012, Vincent Torri wrote:

when using AC_FUNC_ALLOCA, the autoconf documentation says that one should paste some code. That code generates a warning because:

1) the doc says to paste

#elif defined __GNUC__
# define alloca __builtin_alloca

2) the MinGW-w64 compiler already defines alloca in malloc.h, that header files being included by stdlib.h because STDC_HEADERS is defined.

I don't know how to properly fix the doc. One solution would be:

#elif defined __GNUC__
# ifndef alloca
#  define alloca __builtin_alloca
# endif

what do you think ?

I think that your work-around is the safe approach and that the docs should be fixed.

Other build environments (e.g. Solaris 10) also use a similar macro definition and it becomes enabled by the compiler:

#define alloca(x)       __builtin_alloca(x)

Bob Friesenhahn
GraphicsMagick Maintainer,

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