Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!hc!lll-winken!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: calloc
Message-ID: <1428@auspex.auspex.com>
Date: 12 Apr 89 17:45:06 GMT
References: <22842@shemp.CS.UCLA.EDU>
Reply-To: guy@auspex.auspex.com (Guy Harris)
Distribution: na
Organization: Auspex Systems, Santa Clara
Lines: 15

>According to Harbison + Steele's book, calloc returns a region of
>memory with all bits set to zero. They also point out that pointers
>filled with zero bits do not necessarily have the value NULL, nor
>do arithmetic values consisting of zero bits have necessarily have the value 
>zero. How can this be?

Easy.  Consider a machine where the architects, or implementors of
languages available before C was made available, decided that a null
pointer was, say, a bit pattern with the value 0xff000000.  Now, in
order to be compatible with those other languages, the implementors of C
made the bit pattern for a null pointer 0xff000000 as well.

>I always thought a pointer consisting of zero bits is NULL. 

Nope.  No such guarantee was ever made by any C language spec.