From 7561941693920218387 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,b05362a7d4392b67,start X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2000-12-28 17:19:03 PST Path: supernews.google.com!sn-xit-02!supernews.com!newsfeed.online.be!newsfeeds.belnet.be!news.belnet.be!newsfeed.icl.net!dispose.news.demon.net!demon!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: Hubert Matthews Newsgroups: comp.std.c++ Subject: Definition of input iterators Date: Fri, 29 Dec 2000 01:18:02 GMT Organization: Oxyware Ltd Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <3A49DDCC.86CCDD18@oxyware.com> X-Trace: mail2news.demon.co.uk 978052690 mail2news:11144 mail2news mail2news.demon.co.uk X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Accept-Language: en MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-MDaemon-Deliver-To: std-c++@ncar.ucar.edu Lines: 29 Xref: supernews.google.com comp.std.c++:3126 I've found what I consider to be a problem with the definition of input iterators in the Standard. Table 72 states that incrementing an iterator (using either prefix or postfix ++) may invalidate any copies of that iterator. This is a problem when implementing operator++(int), as it must return a copy of the pre-increment value of the iterator which may now not be dereferenceable because of the increment. Table 72 defines the effect of *r++ to be { T tmp = *r; r++; return tmp; }. How is this to be achieved with a user-defined iterator since *r++ must, by the rules of operator precendence, be evaluated as operator++(int) followed by applying operator*() to a potentially invalidated iterator? My suggestion is that incrementing an iterator should guarantee that copies of that iterator are still dereferenceable but not necessarily incrementable. This allows the return from operator++(int) to be used safely. Any takers, or am I being overly fussy? Hubert --- [ 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://www.research.att.com/~austern/csc/faq.html ] [ Note that the FAQ URL has changed! Please update your bookmarks. ]