From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mail4-relais-sop.national.inria.fr (mail4-relais-sop.national.inria.fr [192.134.164.105])
	by walapai.inria.fr (8.13.6/8.13.6) with ESMTP id p7GGYbdq026377
	for <caml-list@sympa-roc.inria.fr>; Tue, 16 Aug 2011 18:34:37 +0200
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AosBAN2aSk7RVaE2kGdsb2JhbABBqDYIFAEBAQEJCQ0HFAQhgUABAQEBAxICLAEbHAIDDAYFCw0JFg8JAwIBAgEREQEFARwHDAgCHodQm0UKjDeCVYU2O4htAgMGhkIEh1mLOYUMgSiGJTyDYw
X-IronPort-AV: E=Sophos;i="4.68,234,1312149600"; 
   d="scan'208";a="105606051"
Received: from mail-fx0-f54.google.com ([209.85.161.54])
  by mail4-smtp-sop.national.inria.fr with ESMTP/TLS/RC4-SHA; 16 Aug 2011 18:34:34 +0200
Received: by fxe4 with SMTP id 4so196655fxe.27
        for <caml-list@inria.fr>; Tue, 16 Aug 2011 09:34:34 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=gamma;
        h=message-id:date:from:user-agent:mime-version:to:subject:references
         :in-reply-to:x-enigmail-version:content-type
         :content-transfer-encoding;
        bh=q9vcLEWJjkGUQf4QZILkbzE7eGvDN4ouofP0DWlHpC4=;
        b=uipBKj0x+mdoTQVWw3d6w05vWpTv00P2DEHFdqKUbfsSTT5r0tM1StvscW6JehVDZL
         YfKrlWU8xGXqX5TEWQylmUXOseyomE8PO9u9Gea8uc+QBsP6y/gtHLJPD0ATlphn4Rf8
         Bi0Ib/X/QMIad8ANpY6GfdgUp0M3aQNFnnBss=
Received: by 10.223.58.75 with SMTP id f11mr7454277fah.70.1313512474423;
        Tue, 16 Aug 2011 09:34:34 -0700 (PDT)
Received: from [192.168.1.101] ([79.114.94.185])
        by mx.google.com with ESMTPS id 16sm146817faw.18.2011.08.16.09.34.32
        (version=SSLv3 cipher=OTHER);
        Tue, 16 Aug 2011 09:34:32 -0700 (PDT)
Message-ID: <4E4A9C17.7060605@gmail.com>
Date: Tue, 16 Aug 2011 19:34:31 +0300
From: =?ISO-8859-1?Q?T=F6r=F6k_Edwin?= <edwintorok@gmail.com>
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110626 Icedove/3.1.11
MIME-Version: 1.0
To: caml-list@inria.fr, rich@annexia.org
References: <CAMT7qiQFZysrnMoKMdmG7eK0CBMkdP=NYgymmqXokJxLuQdWZA@mail.gmail.com> <20110816152550.GA21081@annexia.org> <20110816155137.GA18365@ccellier.rd.securactive.lan> <20110816161042.GA31932@annexia.org> <CAMT7qiSATQcrziJNLp8U=Lwtaj78HFdhgiRd34qJCJOurK0s-g@mail.gmail.com> <20110816162205.GC31932@annexia.org> <20110816162719.GD31932@annexia.org>
In-Reply-To: <20110816162719.GD31932@annexia.org>
X-Enigmail-Version: 1.1.2
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Caml-list] Interfacing with C: bad practice

On 08/16/2011 07:27 PM, Richard W.M. Jones wrote:
> Grrr now _my_ program has a bug.
> 
> ----------------------------------------------------------------------
> #include <stdio.h>
> #include <stdlib.h>
> 
> void f (int a, int b);
> int g (void);
> int *global = NULL;
> 
> int
> main (void)
> {
>   int x = 1;
>   global = &x;
>   f (g (), x);
> 
>   exit (0);
> }
> 
> void
> f (int a, int b)
> {
>   printf ("a = %d, b = %d\n", a, b);
> }
> 
> int
> g (void)
> {
>   if (global) {
>     (*global)++;
>     return *global;
>   }
>   else
>     return 42;
> }
> ----------------------------------------------------------------------
> 
> This program doesn't show undefined behaviour.

Undefined behaviour doesn't mean it must show different results with -O2,
it *might* if the compiler decides to do some optimization.

But isn't this 'f(g(), x)' issue the same as the classic example of undefined behaviour with f(++i, ++i)?

Best regards,
--Edwin