From 412909199891997374 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,221e73cda6c65dc7,start X-Google-Attributes: gidf78e5,public From: "Boris" Subject: relational operators and pointers Date: 2000/06/21 Message-ID: <8iog9l$2bo$1@news.rrz.Uni-Koeln.DE>#1/1 X-Deja-AN: 636915605 Approved: Fergus Henderson , moderator of comp.std.c++ X-Priority: 3 X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Trace: mail2news.demon.co.uk 961529385 mail2news:16676 mail2news mail2news.demon.co.uk Organization: GTEmail.net X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-MSMail-Priority: Normal NNTP-Posting-Date: 20 Jun 2000 19:22:29 GMT Newsgroups: comp.std.c++ The C++ Standard says somewhere: "For templates greater, less, greater_equal, and less_equal, the specializations for any pointer type yield a total order, even if the built-in operators <, >, <=, >= do not." Does this implicitly mean that == and != are ok for comparing pointers no matter what pointers are compared? Somewhere else I found: "If two pointers p and q of the same type point to the same object or function [...] then p<=q and p>=q both yield true and pq both yield false." This is in C++: A *p1 = new A; A *p2 = p1; p1 == p2; // true p1 != p2; // false But then the Standard says: "If two pointers p and q of the same type point to different objects that are not members of the same object [...] the results of pq, p<=q, and p>=q are unspecified." In C++: A *p1 = new A; A *p2 = new A; p1 == p2; // unspecified p1 != p2; // unspecified 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)? Boris --- [ 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 ]