From: Erik Trulsson <ertr1013@student.uu.se>
To: Joe Buck <Joe.Buck@synopsys.COM>
Cc: Dave Korn <dave.korn@artimi.com>,
'Daniel Berlin' <dberlin@dberlin.org>,
mrc.lrn@inwind.it, gcc@gcc.gnu.org
Subject: Re: Pointers in comparison expressions
Date: Tue, 12 Jul 2005 22:28:00 -0000 [thread overview]
Message-ID: <20050712222847.GA90522@falcon.midgard.homeip.net> (raw)
In-Reply-To: <20050712220854.GA7068@synopsys.com>
On Tue, Jul 12, 2005 at 03:08:54PM -0700, Joe Buck wrote:
> On Tue, Jul 12, 2005 at 11:42:23PM +0200, Erik Trulsson wrote:
> > Pointer subtraction is only well defined if both pointers point to elements
> > in the same array (or one past the end of the array). Otherwise the
> > behaviour is undefined.
>
> While this is correct, there are certain cases that the standard leaves
> undefined but that nevertheless can be useful; for example, pointer
> subtraction can be used to estimate the amount of stack in use (of
> course, it is necessary to know if the stack grows upward or downward).
>
> Similarly, in an OS kernel, comparing pointers may make sense.
Yes, there are some situations where it can be useful to compare pointers
to different objects, but then you need to make sure that the compiler you
use actually supports that.
I believe most C compilers support it in practice, but few, if any, have
actually documented it as a supported extension to C.
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
next prev parent reply other threads:[~2005-07-12 22:28 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-12 16:24 Mirco Lorenzoni
2005-07-12 16:32 ` Daniel Berlin
2005-07-12 16:53 ` Dave Korn
2005-07-12 21:00 ` Andreas Schwab
2005-07-12 21:42 ` Erik Trulsson
2005-07-12 22:09 ` Joe Buck
2005-07-12 22:28 ` Erik Trulsson [this message]
2005-07-12 22:38 ` Falk Hueffner
2005-07-12 23:17 ` Joe Buck
2005-07-12 23:28 ` Falk Hueffner
2005-07-13 2:02 ` Joe Buck
2005-07-13 21:42 ` Olivier Galibert
2005-07-12 23:27 ` Michael Meissner
2005-07-12 22:46 ` Joe Buck
2005-07-16 11:49 ` Vincent Lefevre
2005-07-17 16:55 ` Paul Koning
2005-07-18 1:49 ` Vincent Lefevre
2005-07-18 3:13 ` D. Hugh Redelmeier
2005-07-18 13:13 ` Paul Koning
2005-07-18 13:09 ` Paul Koning
2005-07-12 17:03 ` chris jefferson
2005-07-12 23:18 ` Michael Meissner
2005-07-22 23:20 ` Geoffrey Keating
2005-07-13 13:53 Morten Welinder
2005-07-24 1:13 Paul Schlie
2005-07-26 4:43 ` Geoff Keating
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