Re: kfree(0) - ok?

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On Aug 15, 2007, at 06:20:27, Jan Engelhardt wrote:
On Aug 15 2007 11:58, Rene Herman wrote:
NULL is not 0 though.
It is.  Its representation isn't guaranteed to be all-bits-zero,

He said the null _pointer_ isn't guaranteed to be all-bits zero. And it isn't. Read the standard or the faq.

0 is all-bits-zero.
NULL is 0. ("It is.", above)

Transitively, this would make NULL all-bits-zero. I might have missed something, though, perhaps that the cast to void* makes it intransitive. But leave it at whatever the standard says.

but the constant value 0 when used in pointer context is always a null pointer (and in fact the standard requires that NULL be #defined as 0 or a cast thereof).

Irrespective of whatever the standard says, EVERY platform and compiler anybody makes nowadays has a NULL pointer value with all bits clear. Theoretically the standard allows otherwise, but such a decision would break so much code. Linux especially, we rely on the uninitialized data to have all bits clear and we depend on that producing NULL pointers; if a NULL pointer was not bitwise exactly 0 then the test "if (some_ptr != NULL)" would fail and we would start dereferencing garbage.

Cheers,
Kyle Moffett

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