Path: utzoo!attcan!uunet!aplcen!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.unix.wizards
Subject: Re: What machines core dump on deref of NULL?
Message-ID: <13318@smoke.BRL.MIL>
Date: 8 Jul 90 06:07:02 GMT
References: <418@minya.UUCP> <1990Jul6.152722.5320@eng.umd.edu> <9361@rice-chex.ai.mit.edu>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 22

In article <9361@rice-chex.ai.mit.edu> bson@rice-chex.ai.mit.edu (Jan Brittenson) writes:
>>Distinguishable in this sense just means you can use tests like
>>p=0;
>>if (p == &someobject)
>>	code();
>>else
>>	othercode()
>>which will always fail

Correct, and that is the primary reason why the C standard requires
that a null pointer not compare equal to a pointer to any object.

>   Not if someobject resides at address 0, in which case p does point
>to an object.

A conforming C implementation cannot allocate someobject at such as
address that a pointer to it is indistinguishable from a null pointer.

A (not strictly conforming) application may, through appropriate
implementation-specific manipulations, produce such an object pointer,
but what it points to will not qualify as an "object" in the sense in
which the term is used in the C standard.