From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-116663-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 14045 invoked by alias); 1 Jul 2005 09:17:12 -0000
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
Received: (qmail 13986 invoked by uid 22791); 1 Jul 2005 09:17:06 -0000
Received: from serenity.mcc.ac.uk (HELO serenity.mcc.ac.uk) (130.88.200.93)
    by sourceware.org (qpsmtpd/0.30-dev) with ESMTP; Fri, 01 Jul 2005 09:17:06 +0000
Received: from compsoc.umu.man.ac.uk ([130.88.22.5] helo=mrtall.compsoc.man.ac.uk)
	by serenity.mcc.ac.uk with esmtp (Exim 4.43 (FreeBSD))
	id 1DoHdw-000Hoz-6U; Fri, 01 Jul 2005 10:17:04 +0100
Received: from cow by mrtall.compsoc.man.ac.uk with local (Exim 3.36 #1)
	id 1DoHdw-000ItQ-00; Fri, 01 Jul 2005 10:17:04 +0100
Date: Fri, 01 Jul 2005 09:17:00 -0000
From: Jonathan Wakely <cow@compsoc.man.ac.uk>
To: Etienne Lorrain <etienne_lorrain@yahoo.fr>
Cc: gcc@gcc.gnu.org
Subject: Re: sizeof() function parameter array: known problem?
Message-ID: <20050701091703.GA71453@compsoc.man.ac.uk>
References: <20050701084519.9199.qmail@web26907.mail.ukl.yahoo.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20050701084519.9199.qmail@web26907.mail.ukl.yahoo.com>
User-Agent: Mutt/1.4.2.1i
X-UoM: Scanned by the University Mail System. See http://www.mcc.ac.uk/cos/email/scanning for details.
X-SW-Source: 2005-07/txt/msg00027.txt.bz2

On Fri, Jul 01, 2005 at 10:45:19AM +0200, Etienne Lorrain wrote:

>   The result of this funtion is 1, is there a C lawyer around?

The parameter is treated as unsigned* since an array is converted to
a pointer when passed through a function.

C99 says in 6.7.5.3:

   [#7] A declaration of a parameter as ``array of type'' shall
   be adjusted to ``qualified pointer to type'', where the type
   qualifiers (if any) are those specified within the [  and  ]
   of  the  array  type derivation.

> $ cat tmp.c
> unsigned fct (unsigned array[10])

These prototypes are all equivalent, and any sized array (or just a
plain pointer) can be passed to them:

    unsigned fct (unsigned array[10]);
    unsigned fct (unsigned array[]);
    unsigned fct (unsigned* array);

> {
>         return sizeof(array) / sizeof(array[0]);
> }

Therefore what you're testing is sizeof(unsigned*)/sizeof(unsigned)
which is 1 on x86 and most other 32-bit targets (but 2 on e.g. x86_64)

Hope that helps,

jon