From owner-freebsd-current@FreeBSD.ORG  Thu Jul 10 12:00:44 2003
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 6330137B401
	for <current@freebsd.org>; Thu, 10 Jul 2003 12:00:44 -0700 (PDT)
Received: from kientzle.com (h-66-166-149-50.SNVACAID.covad.net
	[66.166.149.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 8B81A43F75
	for <current@freebsd.org>; Thu, 10 Jul 2003 12:00:43 -0700 (PDT)
	(envelope-from kientzle@acm.org)
Received: from acm.org ([66.166.149.53])
	by kientzle.com (8.12.9/8.12.9) with ESMTP id h6AJ0hgY011387;
	Thu, 10 Jul 2003 12:00:43 -0700 (PDT)
	(envelope-from kientzle@acm.org)
Message-ID: <3F0DB887.1080504@acm.org>
Date: Thu, 10 Jul 2003 12:03:35 -0700
From: Tim Kientzle <kientzle@acm.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.0.1) Gecko/20021005
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: David Leimbach <leimy2k@mac.com>
References: <6006001.1057858723473.JavaMail.leimy2k@mac.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
cc: Luigi Rizzo <rizzo@icir.org>
cc: current@freebsd.org
Subject: Re: what is the suggested way to do void * arithmetic ?
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
Reply-To: kientzle@acm.org
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 10 Jul 2003 19:00:44 -0000

David Leimbach wrote:
> I think C takes a more low-level approach and says "void * is just an address
> void * + 1 means the next valid address".

This is not true.

The ANSI C standard forbids arithmetic on void * pointers,
just as C++ does.

GNU gcc has supported void * arithmetic for a long
time as an extension, but it's not standard behavior
and you should not rely on it.

Tim Kientzle