David Robinson wrote:
> 
> On Mon, 1 Jul 1996, Robert S. Thau wrote:
> > 	/*
> >          *  Also, test pointers
> > 	 * against NULL, i.e. use:
> > 	 *
> > 	 * 	(p = f()) == NULL
> > 	 * not:
> > 	 *	!(p = f())
> >          */
> > !foo is used all over the current Apache code.
> 
> This is one that really irritates me (perhaps almost as much as my
> comment style irritates rst 8-( ) because to my mind, '!' takes a boolean
> argument, not a pointer. (Reasons below.)
> 
> But, amazingly, I _can_ actually understand what is meant here.
> Am I the only person who thinks that this discussion has turned into a
> complete waste of time?
> 
>  David.
> 
> Why (!p) is wrong
> -----------------
> 
> As I understand C,
> char *p;
> 
>  if (!p) ...
> 
> is equivalent to
>  if (!(int)p) ...
> 
> Which seems to me to mean something quite different to
>  if (p != NULL) ...

Your understanding is lacking. To quote K&R:

"The operand of the ! operator must have arithmetic type or be a pointer".

> 
> In particular what happens when sizeof(char *) > sizeof(int)
> e.g. Cray or Digital UNIX, or when NULL != (void *)0 (maybe on some
> microsoft systems) ?

Also quoting K&R: "The symbolic constant NULL is often used in place of zero".

> 
> Even if in practice the two test are likely to evaulate to the same
> answer, it does seem like sloppy programming to me.
> 
> 

Cheers,

Ben.

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Ben Laurie                  Phone: +44 (181) 994 6435
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