From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5848 invoked by alias); 4 Feb 2004 15:59:09 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 5827 invoked from network); 4 Feb 2004 15:59:08 -0000 Received: from unknown (HELO nevyn.them.org) (66.93.172.17) by sources.redhat.com with SMTP; 4 Feb 2004 15:59:08 -0000 Received: from drow by nevyn.them.org with local (Exim 4.30 #1 (Debian)) id 1AoPQi-0003KR-DP for ; Wed, 04 Feb 2004 10:59:08 -0500 Date: Wed, 04 Feb 2004 15:59:00 -0000 From: Daniel Jacobowitz To: gdb-patches@sources.redhat.com Subject: Re: [patch/rfc] Test struct0 Message-ID: <20040204155907.GA4130@nevyn.them.org> Mail-Followup-To: gdb-patches@sources.redhat.com References: <40203797.8010607@gnu.org> <20040204004620.GA9431@nevyn.them.org> <40211529.3020504@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40211529.3020504@gnu.org> User-Agent: Mutt/1.5.1i X-SW-Source: 2004-02/txt/msg00075.txt.bz2 On Wed, Feb 04, 2004 at 10:52:09AM -0500, Andrew Cagney wrote: > >On Tue, Feb 03, 2004 at 07:06:47PM -0500, Andrew Cagney wrote: > > > >>Hello, > >> > >>This adds a test for: > >> > >> struct foo0 { }; > >> > >>to the structs.exp testcase (I'm assuming that this is legal ISO-C), it > > > > > >Nope. > > I guess I misunderstood Jim's comments. > http://sources.redhat.com/ml/gdb-patches/2004-01/msg00717.html Hmm, the comment isn't very clear. Yes, this is a GNU extension (though not many people seem to know it). > > struct-or-union-specifier: > > struct-or-union identifier-opt { struct-declaration-list } > > struct-or-union identifier > > > > struct-or-union: > > struct > > union > > > > struct-declaration-list: > > struct-declaration > > struct-declaration-list struct-declaration > > > > struct-declaration: > > specifier-qualifier-list struct-declarator-list ; > > > >So there must be a minimum of one declarator and trailing semicolon > >inside the braces. GCC will warn about this if you ask it to - it's > >probably -ansi, or -std=c89 -ansi -pedantic. > > >While it's not legal C, I believe that it is legal C++. > > But are you sure? :-) If it's legal C++ then it, along with some other > wierd-o edge cases should probably be added to a gdb.cp/struct0 test > (someone with less rusty C++ than me can probably come up with a list). > > Trying to include it in structs.exp would just be too messy. Yeah. Of course, there's the interesting property that zero-element structures have non-zero size in C++. That's because they're a first-class part of the language. Consider: struct foo { }; struct foo bar[10]; int baz = sizeof (bar); In GNU C, baz is initialized to zero. In GNU C++ (i386-linux, but I think all targets since the v3 ABI covers this), baz is initialized to ten. One byte per zero-sized struct is wasted in order to preserve monotonically increasing array element addresses. Then, in some cases (all dealing with base classes), the one byte is optimized away again. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer