Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!munnari.oz.au!csc!bdm659
From: bdm659@csc.anu.oz
Newsgroups: comp.std.c
Subject: Re: null pointers - I was wrong, but not for that reason.
Message-ID: <878.2549e5f7@csc.anu.oz>
Date: 28 Oct 89 17:46:30 GMT
References: <11380@smoke.BRL.MIL> <8952@goofy.megatest.UUCP> <872.254895b5@csc.anu.oz> <30809@watmath.waterloo.edu>
Organization: Computer Services, Australian National University
Lines: 24

From my original posting:
> :    Section 3.2.2.3 (on the result of casting 0 to a pointer type):
> :          "Such a pointer, called a null pointer, is guaranteed not to
> :           point to any object or function."
> :    Section 3.3.9 (on pointer equality):
> :          "If two pointers to object or incomplete types compare equal,
> :           they point to the same object."
> :From these two rules, it logically follows that  (int*)0 != (int*)0 .

From David Tanguay:
> (int *) 0 is not a pointer to an object, so section 3.3.9 doesn't come
> into play.

From Joe English:
> [(A and B point to an object) and (A == B)] ==> [it is the same object].
>   (1)                             (2)           (3)
> If (1) is false it does not follow that (2) is false.

If the sentence is still exactly as I quote it, it only requires pointers to
object types, not pointers to objects.  The difference is quite important.
(I'm learning, TWW.)  See my reply to Doug Gwyn for a more detailed discussion,
and also the REAL reason why I WAS WRONG.

Brendan McKay.