C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  operator++() for iterator          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Alex Vinokur Guest Posted: Tue Aug 08, 2006 9:10 am    Post subject: operator++() for iterator Dinkumware, Ltd. - Compleat Libraries Reference <iterator> http://www.dinkumware.com/manuals/?manual=compleat&page=iterator.html ====================================== back_insert_iterator::operator++ -------------------------------- back_insert_iterator& operator++(); back_insert_iterator operator++(int); The member functions both return *this. ====================================== Question-1. Why do operator++'s return not actually value++, but *this? Question-2. If operator++(int) returns *this, why doesn't it return reference, but value? In other words, why not back_insert_iterator& operator++(int)? ====================================== insert_iterator::operator++ -------------------------------- insert_iterator& operator++(); insert_iterator& operator++(int); The member functions both return *this. ====================================== Here operator++(int) returns reference, not value. What is the difference between * back_insert_iterator::operator++(int) and * insert_iterator::operator++(int) in that context? Alex Vinokur email: alex DOT vinokur AT gmail DOT com http://mathforum.org/library/view/10978.html http://sourceforge.net/users/alexvn [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Earl Purple Guest Posted: Fri Aug 11, 2006 5:43 pm    Post subject: Re: operator++() for iterator Alex Vinokur wrote: Quote: Question-1. Why do operator++'s return not actually value++, but *this? because the return value can be used in a place where an l-value is required Quote: Question-2. If operator++(int) returns *this, why doesn't it return reference, but value? operator++(int) is post-increment, so the value of *this is modified but the original value is used for the expression. Thus it needs to make a copy. It is not technically possible to postpone the modification (for a user-defined type) until after execution of the statement so this acts as a sort-of workaround. In other words, why not Quote: back_insert_iterator& operator++(int)? ====================================== insert_iterator::operator++ -------------------------------- insert_iterator& operator++(); insert_iterator& operator++(int); The member functions both return *this. ====================================== Here operator++(int) returns reference, not value. back_insert_iterator is a cheat though. operator++ here does nothing (both post-increment and pre-increment), it is just there to allow it to work in algorithms. So it is ok for it to return *this rather than a copy, and there is no need to make a copy even for post-increment so they don't. Quote: What is the difference between * back_insert_iterator::operator++(int) and * insert_iterator::operator++(int) in that context? None. Nor is there any difference with not calling it at all, but it's there because algorithms need it. Compilers probably treat it as a no-op and strip it out altogether. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ Language (Moderated) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.