1# serial 5
2# Check for flexible array member support.
3
4# Copyright (C) 2006, 2009-2020 Free Software Foundation, Inc.
5# This file is free software; the Free Software Foundation
6# gives unlimited permission to copy and/or distribute it,
7# with or without modifications, as long as this notice is preserved.
8
9# Written by Paul Eggert.
10
11AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
12[
13  AC_CACHE_CHECK([for flexible array member],
14    ac_cv_c_flexmember,
15    [AC_COMPILE_IFELSE(
16       [AC_LANG_PROGRAM(
17          [[#include <stdlib.h>
18            #include <stdio.h>
19            #include <stddef.h>
20            struct m { struct m *next, **list; char name[]; };
21            struct s { struct s *p; struct m *m; int n; double d[]; };]],
22          [[int m = getchar ();
23            size_t nbytes = offsetof (struct s, d) + m * sizeof (double);
24            nbytes += sizeof (struct s) - 1;
25            nbytes -= nbytes % sizeof (struct s);
26            struct s *p = malloc (nbytes);
27            p->p = p;
28            p->m = NULL;
29            p->d[0] = 0.0;
30            return p->d != (double *) NULL;]])],
31       [ac_cv_c_flexmember=yes],
32       [ac_cv_c_flexmember=no])])
33  if test $ac_cv_c_flexmember = yes; then
34    AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [],
35      [Define to nothing if C supports flexible array members, and to
36       1 if it does not.  That way, with a declaration like 'struct s
37       { int n; short d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack
38       can be used with pre-C99 compilers.
39       Use 'FLEXSIZEOF (struct s, d, N * sizeof (short))' to calculate
40       the size in bytes of such a struct containing an N-element array.])
41  else
42    AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])
43  fi
44])
45