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re PR c++/11072 (Implementation of offsetof macro)

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PR c++/11072
	* ginclude/stddef.h (offsetof): Remove cast to 'char &'. Explain why.
testsuite:
	PR c++/11072
	* g++.dg/other/offsetof2.C: XFAIL.
	* g++.dg/other/offsetof5.C: New.

From-SVN: r68831
This commit is contained in:
Nathan Sidwell 2003-07-02 14:30:53 +00:00 committed by Nathan Sidwell
parent eaac6968d6
commit 300e89a2b6
5 changed files with 47 additions and 8 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,8 @@
2003-07-02 Nathan Sidwell <nathan@codesourcery.com>
PR c++/11072
* ginclude/stddef.h (offsetof): Remove cast to 'char &'. Explain why.
2003-07-02 Andreas Schwab <schwab@suse.de>
* dbxout.c (pending_bincls): Only define if DBX_DEBUGGING_INFO.
@ -6209,6 +6214,7 @@ Fri May 23 21:19:31 CEST 2003 Jan Hubicka <jh@suse.cz>
2003-05-18 Neil Booth <neil@daikokuya.co.uk>
* config/sparc/sparc.h: Define sparc for now.
2003-05-18 Nathanael Nerode <neroden@gcc.gnu.org>
* config.gcc: Clear xm_file, md_file at the beginning of each pass.

24
gcc/ginclude/stddef.h
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@ -409,16 +409,26 @@ typedef __WINT_TYPE__ wint_t;
#ifdef _STDDEF_H
/* Offset of member MEMBER in a struct of type TYPE. */
/* Offset of member MEMBER in a struct of type TYPE. */
#ifndef __cplusplus
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#else /* C++ */
/* The reference cast is necessary to thwart an operator& that might
be applicable to MEMBER's type. See DR 273 for details. */
#define offsetof(TYPE, MEMBER) (reinterpret_cast <size_t> \
(&reinterpret_cast <char &>(static_cast <TYPE *> (0)->MEMBER)))
#endif /* C++ */
#else
/* In C++ a POD type can have a user defined address-of operator, and
that will break offsetof. C++ core defect 273 addresses this and
claims that reinterpret_casts to char & type are sufficient to
overcome this problem.
(reinterpret_cast <size_t>
(&reinterpret_cast <char &>(static_cast <TYPE *> (0)->MEMBER)))
But, such casts are not permitted in integral constant expressions,
which offsetof is supposed to be.
It appears that offsetof is unimplementable in C++ without a
compiler extension. */
#define offsetof(TYPE, MEMBER) (reinterpret_cast <size_t> \
(&static_cast<TYPE *> (0)->MEMBER))
#endif /* C++ */
#endif /* _STDDEF_H was defined this time */
#endif /* !_STDDEF_H && !_STDDEF_H_ && !_ANSI_STDDEF_H && !__STDDEF_H__

4
gcc/testsuite/ChangeLog
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@ -1,5 +1,9 @@
2003-07-02 Nathan Sidwell <nathan@codesourcery.com>
PR c++/11072
* g++.dg/other/offsetof2.C: XFAIL.
* g++.dg/other/offsetof5.C: New.
PR c++/10219
* g++.dg/template/error1.C: New.

4
gcc/testsuite/g++.dg/other/offsetof2.C
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@ -1,4 +1,4 @@
// { dg-do run }
// { dg-do run { xfail *-*-* } }
// { dg-options -Wold-style-cast }
// Copyright (C) 2003 Free Software Foundation, Inc.
@ -6,6 +6,8 @@
// DR273 POD can have an operator&, offsetof is still required to work
// XFAILED - you can't write offsetof without an extension
#include <stddef.h>
struct POD1

17
gcc/testsuite/g++.dg/other/offsetof5.C Normal file
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@ -0,0 +1,17 @@
// { dg-do compile }
// Copyright (C) 2003 Free Software Foundation, Inc.
// Contributed by Nathan Sidwell 30 June 2003 <nathan@codesourcery.com>
// PR c++ 11072, DR 273's solution is broken
#include <stddef.h>
struct F
{
char i;
char j;
};
static int ary[offsetof (F, j)];