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# serial 5
# Check for flexible array member support.
# Copyright (C) 2006, 2009-2019 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
# gives unlimited permission to copy and/or distribute it,
# with or without modifications, as long as this notice is preserved.
# Written by Paul Eggert.
AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
[
AC_CACHE_CHECK([for flexible array member],
ac_cv_c_flexmember,
[AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM(
[[#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>
struct m { struct m *next, **list; char name[]; };
struct s { struct s *p; struct m *m; int n; double d[]; };]],
[[int m = getchar ();
size_t nbytes = offsetof (struct s, d) + m * sizeof (double);
nbytes += sizeof (struct s) - 1;
nbytes -= nbytes % sizeof (struct s);
struct s *p = malloc (nbytes);
p->p = p;
p->m = NULL;
p->d[0] = 0.0;
return p->d != (double *) NULL;]])],
[ac_cv_c_flexmember=yes],
[ac_cv_c_flexmember=no])])
if test $ac_cv_c_flexmember = yes; then
AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [],
[Define to nothing if C supports flexible array members, and to
1 if it does not. That way, with a declaration like 'struct s
{ int n; double d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack
can be used with pre-C99 compilers.
When computing the size of such an object, don't use 'sizeof (struct s)'
as it overestimates the size. Use 'offsetof (struct s, d)' instead.
Don't use 'offsetof (struct s, d@<:@0@:>@)', as this doesn't work with
MSVC and with C++ compilers.])
else
AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])
fi
])
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