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From: wcs@ho95e.ATT.COM (Bill.Stewart)
Newsgroups: news.software.b,comp.lang.c
Subject: Re: News for Xenix on PC AT ?
Message-ID: <1418@ho95e.ATT.COM>
Date: Sat, 25-Apr-87 00:03:34 EDT
Article-I.D.: ho95e.1418
Posted: Sat Apr 25 00:03:34 1987
Date-Received: Sun, 26-Apr-87 20:19:12 EDT
References: <18346@ucbvax.BERKELEY.EDU> <145@sds.UUCP> <17005@sun.uucp> <146@sds.UUCP> <5787@brl-smoke.ARPA>
Reply-To: wcs@ho95e.UUCP (46133-Bill.Stewart,2G218,x0705,)
Organization: AT&T Bell Labs 46133, Holmdel, NJ
Lines: 30
Xref: mnetor news.software.b:544 comp.lang.c:1891

In article <5787@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
:In article <146@sds.UUCP> dave@sds.UUCP (dave schmidt x194) writes:
:-In article <17005@sun.uucp>, guy%gorodish@Sun.COM (Guy Harris) writes:
:-> This last one falls under the heading of "stupid problems from
:-> [censored] compiler writers who didn't understand C before inflicting
:-> something that they claim is a C compiler on Xenix users."
:[  ... much discussion by everyone about differences between
:-> 	if (!charptr) ...		/* Ugly but correct, says Doug	*/
:-> 	if (charptr == 0) ...		/* Best 			*/
:-> 	if (charptr == (char *)0) ...	/* Almost always ok		*/
:-      if ((int)charptr == 0)		/* WRONG, of course		*/
:]
:He, I, and others have explained more than once before in the C newsgroup
:that the only fully correct definition of the macro NULL, as C now stands,
:is as 0.  (Under the proposed ANSI standard you could probably get away
:with defining it as (void *)0.)

Be careful saying this: it's only correct when you're using NULL in
	if (charptr == NULL)
But (as Guy periodically has to remind VAX-users), you can't
simply use NULL in constructs like:
	foo( arg1, arg2, NULL, arg4);
because subroutine foo() might be expecting an argument of a different
size.  If you #define NULL 0, then you pass foo sizeof(int) bytes;
if you #define NULL (void *)0, then you pass it sizeof(void *) bytes.
If you're passing NULL (or other non-int constants), always cast to
	foo( arg1, arg2, (whatever_type) NULL, arg4);
	so the routine receives what you passed.
-- 
# Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs