Document empty structures

[Geoffrey Keating <gkeating at apple dot com>]

This adds documentation of GCC's empty structure extension.

Tested with 'make info'.  I'll apply to both HEAD and 3.3.

-- 
- Geoffrey Keating <geoffk at apple dot com>

===File ~/patches/gcc-emptystructdoc.patch==================
2003-04-11  Geoffrey Keating  <geoffk at apple dot com>

	* doc/extend.texi (Empty Structures): New.

Index: doc/extend.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/extend.texi,v
retrieving revision 1.128
diff -u -p -u -p -r1.128 extend.texi
--- doc/extend.texi	7 Apr 2003 07:31:47 -0000	1.128
+++ doc/extend.texi	12 Apr 2003 01:37:45 -0000
@@ -436,6 +436,7 @@ extensions, accepted by GCC in C89 mode 
 * Hex Floats::          Hexadecimal floating-point constants.
 * Zero Length::         Zero-length arrays.
 * Variable Length::     Arrays whose length is computed at run time.
+* Empty Structures::    Structures with no members.
 * Variadic Macros::	Macros with a variable number of arguments.
 * Escaped Newlines::    Slightly looser rules for escaped newlines.
 * Multi-line Strings::  String literals with embedded newlines.
@@ -1357,6 +1358,21 @@ struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @}
 struct bar c = @{ @{ 1, @{ @} @} @};            // @r{Valid.}
 struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @};  // @r{Invalid.}
 @end example
+
+ at node Empty Structures
+ at section Structures With No Members
+ at cindex empty structures
+ at cindex zero-size structures
+
+GCC permits a C structure to have no members:
+
+ at example
+struct empty @{
+ at };
+ at end example
+
+The structure will have size zero.  In C++, empty structures are part
+of the language, and the language standard says they have size 1.
 
 @node Variable Length
 @section Arrays of Variable Length
============================================================