# HG changeset patch
# User Paul Eggert <eggert@cs.ucla.edu>
# Date 1162920007 0
# Node ID e35875ded92b186f8ab22873cef009348ce10e80
# Parent  4e434249c068eb80fadf516ae2a135b17dd1015c
* m4/flexmember.m4 (AC_C_FLEXIBLE_ARRAY_MEMBER):
Mention that offsetof should be used instead of sizeof.
From Bruno Haible.

diff --git a/ChangeLog b/ChangeLog
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2006-11-07  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* m4/flexmember.m4 (AC_C_FLEXIBLE_ARRAY_MEMBER):
+	Mention that offsetof should be used instead of sizeof.
+	From Bruno Haible.
+
 2006-11-07  Bruno Haible  <bruno@clisp.org>
 
 	* lib/w32spawn.h (prepare_spawn): Use XNMALLOC instead of xmalloc.
diff --git a/m4/flexmember.m4 b/m4/flexmember.m4
--- a/m4/flexmember.m4
+++ b/m4/flexmember.m4
@@ -41,7 +41,11 @@
       [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; 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)
   fi