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From Martin Sebor <se...@roguewave.com>
Subject Re: Null src pointer in memcpy?
Date Fri, 11 Apr 2008 01:40:22 GMT
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
> 


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