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From: dbrooks@osf.org (David Brooks)
Newsgroups: comp.lang.c
Subject: Re: argv[] terminated by a NULL pointer?
Message-ID: <23292@paperboy.OSF.ORG>
Date: 28 Jun 91 14:29:52 GMT
References: <12187@hub.ucsb.edu> <14603@dog.ee.lbl.gov> <1991Jun28.052339.14611@ringer.cs.utsa.edu>
Sender: news@OSF.ORG
Organization: Open Software Foundation
Lines: 23

djimenez@ringer.cs.utsa.edu (Daniel Jimenez) writes:
|> Who said the null pointer couldn't be -1?

Who's allowed to know?

|> On a system where the null pointer is represented by all bits one,
|> the following statement:
|> ((char *)0) == ((char *)-1) 
|> would be true, since 0 in a pointer context is defined to be
|> the null pointer, and -1 is also the null pointer.
|> They would have the same bit pattern.

Is this strictly true?  I know that the conversion of an *object* of
integral type is allowed to go through an implementation-dependent mapping,
although K&RII (at least) doesn't seem to mention an integer constant.

It would be rather perverse to map (char *)-1 to 0x8129ac60, but I could
imagine a compiler writer wanting to avoid mapping -1 to a value internally
identical to a null pointer.
-- 
David Brooks				dbrooks@osf.org
Systems Engineering, OSF		uunet!osf.org!dbrooks
Composing for a percussion ensemble is like writing an essay in highlighter.