Why NULL is 0

[Dave Sill]

I wrote:
>In article <800 at zippy.eecs.umich.edu> Jan Wolter <janc at palam.eecs.umich.EDU> writes:
>>	char *p2 = zero;          /* is this a null pointer? */
>
>Maybe.  K&R say assignments between pointers and ints are nonportable,
>as are assignments between different types of pointers.
>
>>	char *p3 = (char *)zero;  /* what's this? */
>
>Exactly the same as p2.  K&R define a cast as performing the
>conversions required to assign the operand to a variable of the type
>of the cast.

K&R page 42:
"...	(type-name) expression  ...
The precise meaning of a cast is in fact as if *expression* were
assigned to a variable of the specified type..."

This leads one to the conclusion that
	char *p = zero;
and
	char *p = (char *)zero;
give the same result.  Why, then, does the former cause a warning
about an illegal combination of pointer and integer?  Is the sole
function of the cast in the latter to prevent such a warning?

>>(Frankly,
>>the more I read on this subject, the more I think K&R didn't have their minds
>>entirely clear on this business either.)
>
>Maybe you should read some more.

I'd suggest reading the dpANS-C, where this is all much more
well-defined.

=========
The opinions expressed above are mine.

"Meanings receive their dignity from words instead of giving it to them."
					-- Blaise Pascal