gnulib/import/m4/flexmember.m4

   1 # serial 5
   2 # Check for flexible array member support.
   3
   4 # Copyright (C) 2006, 2009-2019 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
  11 AC_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 ])