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From: grahamr@azure.UUCP (Graham Ross)
Newsgroups: net.lang.c
Subject: Re: Must a NULL pointer be a 0 bit pattern?
Message-ID: <100@azure.UUCP>
Date: Wed, 31-Oct-84 12:51:46 EST
Article-I.D.: azure.100
Posted: Wed Oct 31 12:51:46 1984
Date-Received: Fri, 2-Nov-84 05:32:21 EST
References: <6542@mordor.UUCP> <5272@brl-tgr.ARPA> <196@rlgvax.UUCP>, <529@wjh12.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 19

Three comments about non-zero NULL:

1. Because of implicit comparison with zero, as in "while(p)s;", this idea
is cannot be implemented simply by changing stdio.h to read
#define NULL ((char*)0x87654321)

2. In making changes to the compiler, this must remain zero:
	(p = NULL , (int)p)
Also, for every declared "var", this must remain one:
	(p = &var , (int)p != 0)

3. The issue of how a union can be set to zero was handled properly by the
correspondent who said the first member is initialized to zero.  A further
note might be made that exec(2) need not know where to put the 0x87654321
patterns; crt0 or something emitted by the linker can do this, but perhaps
with a substantial amount of work and/or abandonment by Unix of the
"common model" for linking.

	Graham Ross, Tektronix, ...!tektronix!tekmdp!grahamr