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From: guy@gorodish.UUCP
Newsgroups: comp.lang.c
Subject: Re: pointer debate raging on...  (LONG)
Message-ID: <17446@sun.uucp>
Date: Mon, 27-Apr-87 14:56:13 EDT
Article-I.D.: sun.17446
Posted: Mon Apr 27 14:56:13 1987
Date-Received: Wed, 29-Apr-87 00:48:25 EDT
References: <149@sds.UUCP>
Sender: news@sun.uucp
Reply-To: guy@sun.UUCP (Guy Harris)
Organization: Sun Microsystems, Mountain View
Lines: 41

>Again, this bias of mine comes with working with brain-damaged compilers
>which do not correctly compare 32-bit pointers to 16-bit ints.

Any compiler that thinks that it should be comparing a pointer to an
"int" when confronted with

	if (charptr == 0)

is *prima facie* wrong, regardless of whether pointers and "int"s are
the same size.  The problem is *not* that said compilers weren't
properly comparing pointers and "int"s; the problem is that said
compilers weren't coercing the 0 to (char *)0 and comparing pointers
and pointers.

>Applaud, applaud, applaud.  John has correctly pointed out that
>sizeof(pointer) == sizeof(int)  is not the universal constant that 
>many people believe it to be.  It is for this exact reason that 
>NULL should ***NOT*** be defined as 0.

OK, now given that

	sizeof (char *) == sizeof (int *)

is also not a tautology, what should NULL be defined as?  (char *)0
won't cut it, nor will (int *)0.

If you have function prototypes, function calls - in *most*, but not
*all*, cases - will behave like other operators; the compiler will be
able to properly coerce arguments (*or* complain if the coercion
doesn't make any sense, which is why I like the idea of function
prototypes *and* would prefer that compilers generate warning
messages whenever a function is used and there is no prototype
declaration or definition for that function in scope).  Given this,
as long as you remember to properly cast null pointers passed to
functions like "execl", NULL can be defined as 0.

If you don't have function prototypes, you can stick in the
appropriate cast to coerce NULL into a null pointer of the proper
type.  Given this, NULL can be defined as 0, and probably should,
since "lint" will not be happy about casting a "char *" into, say, an
"int *".