Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!ssc-vax!cxsea!blm
From: blm@cxsea.UUCP (Brian Matthews)
Newsgroups: comp.lang.c
Subject: Re: calloc (actually NULL =?= 0)
Message-ID: <2661@cxsea.UUCP>
Date: 13 Apr 89 19:07:16 GMT
References: <22842@shemp.CS.UCLA.EDU> <1428@auspex.auspex.com> <987@atanasoff.cs.iastate.edu>
Reply-To: blm@cxsea.UUCP (Brian Matthews)
Distribution: na
Organization: Computer X Inc.
Lines: 24

John Hascall (hascall@atanasoff.cs.iastate.edu) writes:
|In article <1428@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes:
|>>According to Harbison + Steele's book, calloc returns a region of
|>>memory with all bits set to zero. They also point out that pointers
|>>I always thought a pointer consisting of zero bits is NULL. 
|>Nope.  No such guarantee was ever made by any C language spec.
|
|   What about the following taken from K&R, Appendix A, section 7.14,
|   "Assignment operator":
|
|       [talking about assigning ints to/from pointers
|       being "a bad thing"] ...
|       However, it is guaranteed that assignment of the
|       constant 0 to a pointer will produce a null pointer...

But this doesn't guarantee that the resulting pointer consists of all
zero bits.  Arbitrary bit fiddling may occur during an assignment
(consider assigning an int to a float, the bits can't be just copied), so
just because you start with all 0 bits doesn't mean you end with all zero
bits.

-- 
Brian L. Matthews  blm@cxsea.UUCP   ...{mnetor,uw-beaver!ssc-vax}!cxsea!blm
+1 206 251 6098    Computer X Inc. - a division of Motorola New Enterprises