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From: alexis@reed.UUCP (Alexis Dimitriadis)
Newsgroups: net.lang.c
Subject: Re: NULL pointer
Message-ID: <2158@reed.UUCP>
Date: Tue, 19-Nov-85 00:27:15 EST
Article-I.D.: reed.2158
Posted: Tue Nov 19 00:27:15 1985
Date-Received: Wed, 20-Nov-85 00:53:13 EST
References: <2098@brl-tgr.ARPA> <916@celtics.UUCP> <2910@sun.uucp> <52@hadron.UUCP> <2982@sun.uucp> <325@steinmetz.UUCP>
Reply-To: alexis@reed.UUCP (Alexis Dimitriadis)
Organization: Reed College, Portland, Oregon
Lines: 33
Summary: 

> 	#define NULL	((char *) 0)
> 
> rather than arithmetic zero. This would make it work on machines which use a
> non-zero null pointer. I have tried doing this in a number of programs to
> examine the effect on lint and/or the generated code, and have yet to find a
> case where it caused a problem (although it did reveal a few genuine bugs in
> "working code").

What exactly did you try?  Defining NULL this way generates _compiler_
errors whenever you use NULL in a context that requires anything other
than a char pointer, e.g. a comparison.  The only case when it _fixes_
things is when NULL is a function argument, and the draft standard will
provide for function argument coercion, as well.  Example:

#include <stdio.h>
#undef NULL
#define NULL ((char *)0)
main()
{
	if (fopen("foo", "w") == NULL)
		;
}
% cc t.c
"t.c", line 8: warning: illegal pointer combination

--Alexis Dimitriadis
-- 
_______________________________________________
  As soon as I get a full time job, the opinions expressed above
will attach themselves to my employer, who will never be rid of
them again.
				alexis @ reed
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