Path: utzoo!attcan!ncrcan!hcr!john
From: john@hcr.uucp (John R. MacMillan)
Newsgroups: comp.lang.c
Subject: Re: references to dereferenced null pointers
Message-ID: <1990Mar15.184903.3397@hcr.uucp>
Date: 15 Mar 90 18:49:03 GMT
References: <51083@microsoft.UUCP> <25EB8EE8.8462@paris.ics.uci.edu> <1990Mar12.175613.12082@utzoo.uucp> <1623@argus.UUCP> <1990Mar14.164539.23685@utzoo.uucp> <16179@haddock.ima.isc.com>
Reply-To: john@troch.UUCP (John R. MacMillan)
Organization: HCR Corporation, Toronto
Lines: 18

Karl Heuer <karl@haddock.ima.isc.com> writes:
|>There is absolutely nothing wrong with having a pointer representation in
|>which the bit pattern for a null pointer is not all zeros... except that
|>there are a lot of old, badly-written programs which will break.  Thus my
|>earlier comment that it is valid but unwise.
|
|Note that "p = 0", "p == 0", "!p", "char *f() { return 0; }" are *not*
|examples of such badly-written code; they may be bad style, but the compiler
|is required to generate correct code involving a true null pointer.  The only
|"dangerous" context (other than hacking with unions and such) is when a null
|pointer constant is being passed as an argument to a function.

``Zeroing out'' pointers with memset, bzero, or calloc is another
all-too-common problem.
-- 
John R. MacMillan	| "All the best freaks are here; please stop staring
HCR Corporation		|  at me."
{utzoo,utcsri}!hcr!john	| -- Marillion