From -8888108702201839892 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,221e73cda6c65dc7 X-Google-Attributes: gidf78e5,public From: Francis Glassborow Subject: Re: relational operators and pointers Date: 2000/06/22 Message-ID: #1/1 X-Deja-AN: 637331785 Approved: Fergus Henderson , moderator of comp.std.c++ References: <8iog9l$2bo$1@news.rrz.Uni-Koeln.DE> X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Trace: mail2news.demon.co.uk 961614363 mail2news:13314 mail2news mail2news.demon.co.uk Organization: Southfield Microcomputer SS X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) MIME-Version: 1.0 Reply-To: Francis Glassborow Newsgroups: comp.std.c++ In article <8iog9l$2bo$1@news.rrz.Uni-Koeln.DE>, Boris writes >But this is stupid as you are allowed only to compare pointers that point to >the same object because the rest is unspecified. That means you have to know >whether pointers point to the same object before you compare them! Do I >misunderstand the Standard (I really hope so)? Possibly (the templates you started with are a red-herring). You are always allowed to compare for equality any two valid pointers (look elsewhere for a discussion for what makes a pointer valid). That means that providing p1 and p2 are valid pointers you can always evaluate p1==p2 and p1!=p2. However you can only apply the other four comparison operators to pointers that point into the same object. The template versions may have to walk on eggshells to get round problems with pointers that do not point to somewhere in the same object. Consider a generalised pointer concept such as a URL, it is easy to check if two URL's result in the same location, but how do you provide a complete ordering (I am not saying this is impossible, just that it is non-trivial unless you know rather more than just that they are two valid URL's) Francis Glassborow Association of C & C++ Users 64 Southfield Rd Oxford OX4 1PA +44(0)1865 246490 All opinions are mine and do not represent those of any organisation --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]