Re: Secure Dereference of NULL-Pointer when using list.h

[Ricard Wanderlof <ricard.wanderlof@xxxxxxxx>]

On Thu, 5 Oct 2006, Jinesh K J wrote:

> But, let us clear things up before leaving the topic off. With
> reference to ISO/IEC 9899:1999(E), the following could be observed:
> ...
> -  value of a void expression shall not be used in any way
> -  If an expression of any other type(which included our variable 'a')
> is evaluated as a void expression, its value or designator is
> discarded.
> -  Here there are no side effects( no function call, assignments, etc)
>
> I hope my observations are correct.

You may be right. Reading standards is hairy and I would also consider the 
interpretation "evaluate the expression and discard the value" valid. 
Although I'm nitpicking here, say if foo were a hardware register which 
had a side effect of some sorts when reading it, then the statement *foo; 
would actually do something even though the value wouldn't be used (better 
declare foo volatile too to make sure the compiler doesn't optimize it 
away).

In any case, I wouldn't like to let a line like

*( (char *) 0);

pass by the compiler, whether or not the actual compiler conforms to the 
standard, whichever the interpretation of the standard may be. It's one of 
the situations that I would imagine a compiler designer could get wrong, 
regardless what the standard says...

/Ricard
--
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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