Mailing-List: contact dev-help@stdcxx.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@stdcxx.apache.org
Received-SPF: pass (nike.apache.org: domain of msebor@gmail.com designates
 209.85.200.174 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=message-id:date:from:organization:user-agent:mime-version:to:subject:references:in-reply-to:content-type:content-transfer-encoding:sender;
        b=qLnJ2cIiH9g+vmZmG4vc0Uv31Puw8OE2QhbvWyOCJc/5WeDGQiA9kRdQzIoOPfQb6BJryakLog1/vnHVg36R8EW4i9tpxUdSa20qzN518S9SrxNCWBVL/KhDdPI3ntacxsY8ah8OvXJNB/yUoYOn0rVScGt/frP3ZA4JIyzzwbs=
Message-ID: <47FEC186.1050901@roguewave.com>
Date: Thu, 10 Apr 2008 19:40:22 -0600
From: Martin Sebor <sebor@roguewave.com>
Organization: Rogue Wave Software, Inc.
User-Agent: Thunderbird 2.0.0.12 (X11/20080226)
MIME-Version: 1.0
To: dev@stdcxx.apache.org
Subject: Re: Null src pointer in memcpy?
References: 
 <CFFDD219128FD94FB4F92B99F52D0A49010A36F0@exchmail01.Blue.Roguewave.Com>
 <47FEBCEC.20609@roguewave.com>
In-Reply-To: <47FEBCEC.20609@roguewave.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: Martin Sebor <msebor@gmail.com>

This is explicitly required in 7.1.4 of C99:

       7.1.4 Use of library functions

   -1- Each of the following statements applies unless explicitly stated
       otherwise in the detailed descriptions that follow: If an argument
       to a function has an invalid value (such as a value outside the
       domain of the function, or a pointer outside the address space
       of the program, or a null pointer, or a pointer to non-modifiable
       storage when the corresponding parameter is not const-qualified)
       or a type (after promotion) not expected by a function with
       variable number of arguments, the behavior is undefined. ...

Here's an answer to the same question on comp.lang.c.moderated:
   http://tinyurl.com/6eqo3n

Martin Sebor wrote:
> Eric Lemings wrote:
>>  
>> Is it safe to pass a null pointer as the 2nd argument to memcpy()?  Or
>> undefined?
> 
> Assuming the third argument is 0. Strictly speaking I believe it's
> undefined because memcpy(s1, s2, n) is specified to "copy n bytes
> from the object pointed to by s2 into the object pointed to by s1"
> and a null pointer doesn't point to an object. An object is defined
> as "a region of storage in the execution environment, the contents
> of which can represent values."
> 
> AFAIK, most implementations allow null pointers for no-op calls to
> memcpy() but gcc issues a warning when it detects at compile time
> that a null pointer is passed as the first or second argument to
> memcpy().
> 
> Martin
>