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From: Schauble@mit-multics.arpa
Newsgroups: comp.lang.c
Subject: Pointer comparison and Portability
Message-ID: <4537@brl-adm.ARPA>
Date: Thu, 19-Feb-87 05:22:26 EST
Article-I.D.: brl-adm.4537
Posted: Thu Feb 19 05:22:26 1987
Date-Received: Fri, 20-Feb-87 01:56:05 EST
Sender: news@brl-adm.ARPA
Lines: 16

Unfortunately, the Intel 8086 series provides another counter example.
On this machine, address are in the form of segment and offset.  The
Actual Address is 16*segment + offset.  This is usually written as
segment:offset.  Thus, the two pointers 0100:0010 and 0101:0000 point at
the same byte.  If compared, they will *NOT* compare equal.

So, if two pointers compare equal, they definately point at the same
object.  However, the converse is not true.  Two pointers that do not
compare equal do NOT (necessarily) point at different objects.

Seems like when K & R says that pointer comparison is undefined except
when the two are pointers to the same array, it should be taken to mean
exactly that for all operators, including == and !=.

          Paul
          Schauble at MIT-Multics.arpa