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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.lang.c
Subject: Re: RE: if(p)
Message-ID: <6070@utzoo.UUCP>
Date: Wed, 23-Oct-85 13:19:43 EDT
Article-I.D.: utzoo.6070
Posted: Wed Oct 23 13:19:43 1985
Date-Received: Wed, 23-Oct-85 13:19:43 EDT
References: <1671@brl-tgr.UUCP> <30000017@ISM780.UUCP> <292@graffiti.UUCP> <2902@sun.uucp>, <334@graffiti.UUCP>
Organization: U of Toronto Zoology
Lines: 16

> Question: isn't this all rather moot? I mean, what sort of architecture could
> you actually run 'C' on that doesn't allow the use of zero as a null pointer?
> If nothing else you can always add a shim at 0000:0000 (or whatever weird
> method you use for indicating segments)...

Shame on you Peter, for not reading the entire net.lang.c archives before
asking this question :-).  Some while ago this very issue was raised:  some
poor people were faced with implementing C on an architecture which did
interesting things with the high-order bits of pointers, such that any
attempt to treat an all-0 value as a pointer caused a trap.  Not just any
attempt to follow the pointer, mind you, but any attempt to do *anything*
with it.  Trapping *NULL is one thing; trapping foo=NULL is unacceptable.
So they could not use all-0 as NULL.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry