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From: das@lanai.cs.ucla.edu (David Smallberg)
Newsgroups: comp.lang.c
Subject: Re: references to dereferenced null pointers
Message-ID: <33141@shemp.CS.UCLA.EDU>
Date: 17 Mar 90 01:47:08 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>
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Reply-To: das@lanai.UUCP (David Smallberg)
Organization: UCLA Computer Science Department
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In article <1990Mar14.164539.23685@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) 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.

I've seen "the constant 0" misinterpreted in this way:

	thing *array[100];

		/* clear array to NULLs */   <-- WRONG
	(void) memset(array,0,sizeof(array));
		or
	(void) memset(array,NULL,sizeof(array));

The offender believes that since he's using the constant 0, the compiler
will use the appropriate bit pattern for a NULL pointer, even if that's not
all-zero-bits.

-- David Smallberg, das@cs.ucla.edu, ...!{uunet,ucbvax,rutgers}!cs.ucla.edu!das