Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!rutgers!seismo!mcvax!ukc!dcl-cs!bath63!pes
From: pes@bath63.UUCP
Newsgroups: comp.lang.c
Subject: Re: Pointer comparison and Portability
Message-ID: <782@bath63.ux63.bath.ac.uk>
Date: Fri, 20-Feb-87 07:47:24 EST
Article-I.D.: bath63.782
Posted: Fri Feb 20 07:47:24 1987
Date-Received: Sun, 22-Feb-87 01:49:41 EST
References: <4537@brl-adm.ARPA>
Reply-To: pes@ux63.bath.ac.uk (Paul Smee)
Organization: AUCC c/o University of Bath
Lines: 19


Well, Multics itself provides the most dangerous of both worlds in that you
can get:

Two pointers of (to all determinable checks) *look* different but which in
fact point to the same thing (because the program has, through some cutesy
trick, managed to get the same 'physical' segment initiated twice, with 2
different 'logical' segment numbers.

Two pointers which (as near as can be determined) are identical, but which
the program 'thinks' (and which are 'supposed to') point at different things
(because the program has gotten a pointer to some 'object', and then managed
to terminate the 'physical' segment, and initiate a new segment, with the
same 'logical' segment number.

Admittedly, both of these effects require some fairly shady programming, but
unfortunately that's not unheard of.  They can also be achieved fairly
easily on large projects involving several programmers and a communication
breakdown.