| 1 | # Check for flexible array member support.
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| 2 |
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| 3 | # Copyright (C) 2006 Free Software Foundation, Inc.
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| 4 |
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| 5 | # This program is free software; you can redistribute it and/or modify
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| 6 | # it under the terms of the GNU General Public License as published by
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| 7 | # the Free Software Foundation; either version 2, or (at your option)
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| 8 | # any later version.
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| 9 |
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| 10 | # This program is distributed in the hope that it will be useful,
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| 11 | # but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | # GNU General Public License for more details.
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| 14 |
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| 15 | # You should have received a copy of the GNU General Public License
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| 16 | # along with this program; if not, write to the Free Software
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| 17 | # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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| 18 | # 02110-1301, USA.
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| 19 |
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| 20 | # Written by Paul Eggert.
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| 21 |
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| 22 | AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
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| 23 | [
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| 24 | AC_CACHE_CHECK([for flexible array member],
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| 25 | ac_cv_c_flexmember,
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| 26 | [AC_COMPILE_IFELSE(
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| 27 | [AC_LANG_PROGRAM(
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| 28 | [[#include <stdlib.h>
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| 29 | #include <stdio.h>
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| 30 | #include <stddef.h>
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| 31 | struct s { int n; double d[]; };]],
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| 32 | [[int m = getchar ();
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| 33 | struct s *p = malloc (offsetof (struct s, d)
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| 34 | + m * sizeof (double));
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| 35 | p->d[0] = 0.0;
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| 36 | return p->d != (double *) NULL;]])],
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| 37 | [ac_cv_c_flexmember=yes],
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| 38 | [ac_cv_c_flexmember=no])])
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| 39 | if test $ac_cv_c_flexmember = yes; then
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| 40 | AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [],
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| 41 | [Define to nothing if C supports flexible array members, and to
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| 42 | 1 if it does not. That way, with a declaration like `struct s
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| 43 | { int n; double d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack
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| 44 | can be used with pre-C99 compilers.
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| 45 | When computing the size of such an object, don't use 'sizeof (struct s)'
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| 46 | as it overestimates the size. Use 'offsetof (struct s, d)' instead.
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| 47 | Don't use 'offsetof (struct s, d@<:@0@:>@)', as this doesn't work with
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| 48 | MSVC and with C++ compilers.])
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| 49 | else
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| 50 | AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], 1)
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| 51 | fi
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| 52 | ])
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