On Aug 21, 2008, at 7:57 AM, Sam Mo wrote:
On Aug 21, 2008, at 4:47 AM, Thomas Engelmeier wrote:
Am 21.08.2008 um 05:03 schrieb Michael Ash:
There was a common perception that NULL is not really the same
as nil. But
seems like in the end it really is (void*)0.
They differ in type, not in value.
"NULL" is (void *) 0.
"nil" is (id) 0.
"Nil" is (Class) 0.
This is true conceptually but not as far as their actual definition.
NULL can be either 0 or (void *)0.
Let's be a little bit more precise, I'll try to paraphrase
correctly from my memory:
a.)
(int) NULL is NOT required or guaranteed 0x0 by the standard.
This is why one should never use
if( anPtr == (void *) 0 );
instead of
if( anPtr == NULL );
On modern machines, it usually is.
But Stroustrup says NULL is defined as 0 (zero) in C++.
<http://www.research.att.com/~bs/bs_faq2.html#null>
With my C++ background, I normally write:
if (thePtr) {
// do things
}
else {
// error handling
}
Btw, I recall reading something in the PPC days that the expected
case should put first so the compiler can optimize better (branch
prediction?).
apparently this is also discussed in C-FAQ:
<http://c-faq.com/null/ptrtest.html>
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