NEWS.stable: log cherry-pick [e446f25]->[c092018] relocatable-shell: Update suggested...

[gnulib.git] / m4 / flexmember.m4

diff --git a/m4/flexmember.m4 b/m4/flexmember.m4
index 2a6ae47..b138550 100644 (file)
--- a/m4/flexmember.m4
+++ b/m4/flexmember.m4
@@ -1,21 +1,10 @@
+# serial 3
 # Check for flexible array member support.
 
-# Copyright (C) 2006 Free Software Foundation, Inc.
-
-# This program is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 2, or (at your option)
-# any later version.
-
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-
-# You should have received a copy of the GNU General Public License
-# along with this program; if not, write to the Free Software
-# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
-# 02110-1301, USA.
+# Copyright (C) 2006, 2009-2014 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.
 
@@ -25,24 +14,28 @@ AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
     ac_cv_c_flexmember,
     [AC_COMPILE_IFELSE(
        [AC_LANG_PROGRAM(
-         [[#include <stdlib.h>
-           #include <stdio.h>
-           #include <stddef.h>
-           struct s { int n; double d[]; };]],
-         [[int m = getchar ();
-           struct s *p = malloc (offsetof (struct s, d)
-                                 + m * sizeof (double));
-           p->d[0] = 0.0;
-           return p->d != (double *) NULL;]])],
+          [[#include <stdlib.h>
+            #include <stdio.h>
+            #include <stddef.h>
+            struct s { int n; double d[]; };]],
+          [[int m = getchar ();
+            struct s *p = malloc (offsetof (struct s, d)
+                                  + m * sizeof (double));
+            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
+       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.])
+       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)
+    AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])
   fi
 ])