Path: utzoo!attcan!uunet!mcvax!hp4nl!ruuinf!piet
From: piet@ruuinf (Piet van Oostrum)
Newsgroups: comp.lang.c
Subject: Re: use of NULL
Keywords: NULL zero 0 C Microsoft
Message-ID: <1153@ruuinf.UUCP>
Date: 23 Feb 89 09:44:31 GMT
References: <1167@unisec.usi.com. <5312@turnkey.TCC.COM. <9582@smoke.BRL.MIL. <399@twwells.uucp: <973@optilink.UUCP>
Sender: piet@ruuinf.UUCP
Reply-To: piet@ruuinf (Piet van Oostrum)
Organization: Dept of Computer Science, University of Utrecht, Holland
Lines: 36
In-reply-to: cramer@optilink.UUCP (Clayton Cramer)

In article <973@optilink.UUCP>, cramer@optilink (Clayton Cramer) writes:
 `In article <399@twwells.uucp:, bill@twwells.uucp (T. William Wells) writes:
 `: In article <965@optilink.UUCP: cramer@optilink.UUCP (Clayton Cramer) writes:
 `: : . Using 0 instead of NULL is perfectly acceptable.
 `: :
 `: : No it isn't.  Segmented architecture machines will have problems with
 `: : that in large model.  Microsoft defines NULL as 0L, not 0, in large
 `: : model.  Pushing an int 0 instead of a long 0 will screw you royally
 `: : on the PC.
 `: 
And on and on and on and on .....

You are all wrong. ANSI C says that the CONSTANT 0 used in a pointer
context should always give the ``null'' pointer for that pointer type.

BUT

It must be clear from the context that a pointer type is required.

The only good way to give a null pointer to a function is to write

		funct ( (foo *) 0 );
                        ^^^^^^^

i.e cast it. If you have function prototypes, the cast will be done by the
compiler. Even if you want to use NULL you have to write:

		funct ( (foo *) NULL );

If you don't cast, it may work on your particular compiler, but some day it
will hit you, unless you throw away your program before anybody else gets a
chance to use it.
-- 
Piet van Oostrum, Dept of Computer Science, University of Utrecht
Padualaan 14, P.O. Box 80.089, 3508 TB Utrecht, The Netherlands
Telephone: +31-30-531806. piet@cs.ruu.nl (mcvax!hp4nl!ruuinf!piet)