Date: Tue, 12 Nov 2002 08:25:12 +0100 (CET) From: Harti Brandt <brandt@fokus.gmd.de> To: David Malone <dwmalone@maths.tcd.ie> Cc: Andrew Gallatin <gallatin@cs.duke.edu>, <FreeBSD-current@FreeBSD.ORG> Subject: Re: gcc 3.2.1 optimization bug ? Message-ID: <20021112082236.Y34632-100000@beagle.fokus.gmd.de> In-Reply-To: <20021111223924.GA30568@walton.maths.tcd.ie>
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On Mon, 11 Nov 2002, David Malone wrote:
DM>On Mon, Nov 11, 2002 at 04:52:22PM +0100, Harti Brandt wrote:
DM>AG>But does using a union make it safe?
DM>
DM>> Well, I just had a long discussion with a collegue about the topic. The
DM>> main problem is in the ISO-C standard, section 6.7 point 4 which states:
DM>>
DM>> All declarations in the same scope that refer to the same object or
DM>> function shall specify compatible types.
DM>
DM>I think Section 6.5 paragraph 7 allows access through unions. There
DM>is a footnote saying that the list given (which includes access
DM>through the same type, qualified versions of the same type, aggregates
DM>and unions containign that type and character types) is intended
DM>for determining aliasing rules.
That just allows you to do
int foo
union bar {
int foofoo;
} *ptr = (union bar)&foo;
I think. You end up with the same situation - you can refer the integer
object foo only through an integer pointer.
harti
--
harti brandt, http://www.fokus.gmd.de/research/cc/cats/employees/hartmut.brandt/private
brandt@fokus.gmd.de, brandt@fokus.fhg.de
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