# serial 5

# Check for flexible array member support.

# Copyright (C) 2006, 2009-2020 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; short d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack

       can be used with pre-C99 compilers.

       Use 'FLEXSIZEOF (struct s, d, N * sizeof (short))' to calculate

       the size in bytes of such a struct containing an N-element array.])

  else

    AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])

  fi

])