C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  vector of references          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message dragoncoder Guest Posted: Sat Jul 23, 2005 10:04 am    Post subject: vector of references Hello all, I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? How is a vector of this sort initialized, as references need to be initialized when they are defined. In short my question is "What does such a vector contain ?". /P [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maxim Yegorushkin Guest Posted: Sat Jul 23, 2005 1:43 pm    Post subject: Re: vector of references On Sat, 23 Jul 2005 14:04:15 +0400, dragoncoder <pktiwary (AT) gmail (DOT) com> wrote: Quote: I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? How is a vector of this sort initialized, as references need to be initialized when they are defined. References have wrong assignment sematics for vector. They are only initialized as pointers, but behave as objects. Quote: In short my question is "What does such a vector contain ?". You can't use vector of references in practice, so the question makes little sense. -- Maxim Yegorushkin <firstname.lastname (AT) gmail (DOT) com> [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jakob Bieling Guest Posted: Sat Jul 23, 2005 1:44 pm    Post subject: Re: vector of references "dragoncoder" <pktiwary (AT) gmail (DOT) com> wrote Quote: Hello all, I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? How is a vector of this sort initialized, as references need to be initialized when they are defined. In short my question is "What does such a vector contain ?". You cannot have a vector of references, as references cannot be re-assigned. Once you intialized the reference, it will always reference the same object. So references do not meet the requirements for a type that a vector can hold. regards -- jb (reply address in rot13, unscramble first) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Tutone Guest Posted: Sun Jul 24, 2005 11:24 am    Post subject: Re: vector of references dragoncoder wrote: Quote: I heard STL containers use copy semantics True. Quote: If thats the case, what is the meaning of a vector declaration parameterized on references? How is a vector of this sort initialized, as references need to be initialized when they are defined. In short my question is "What does such a vector contain ?". If you try to compile the following very short program, I believe that all your questions will be answered: #include <vector> int main() { std::vector<int&> refVec; } Best regards, Tom [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Pete Becker Guest Posted: Sun Jul 24, 2005 11:30 am    Post subject: Re: vector of references dragoncoder wrote: Quote: Hello all, I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? Try it. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.com) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top James Kanze Guest Posted: Sun Jul 24, 2005 11:40 am    Post subject: Re: vector of references dragoncoder wrote: Quote: I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? Undefined behavior. References do not meet the requirements for the instantiation type of std::vector. -- James Kanze mailto: [email]james.kanze (AT) free (DOT) fr[/email] Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 pl. Pierre Sémard, 78210 St.-Cyr-l'École, France +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Tutone Guest Posted: Sun Jul 24, 2005 11:35 pm    Post subject: Re: vector of references James Kanze wrote: Quote: dragoncoder wrote: I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? Undefined behavior. References do not meet the requirements for the instantiation type of std::vector. I would go even further. Although technically a vector of references may result in undefined behavior, I don't think that a standard-conforming compiler and library could even compile a program purporting to include such a constuct, because it would involve a reference to a reference. At any rate, I tried it on three compilers, and all choked. Best regards, Tom [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Mon Jul 25, 2005 3:19 pm    Post subject: Re: vector of references Thomas Tutone wrote: Quote: James Kanze wrote: dragoncoder wrote: I heard STL containers use copy semantics i.e they keep a copy of the original object. If thats the case, what is the meaning of a vector declaration parameterized on references? Undefined behavior. References do not meet the requirements for the instantiation type of std::vector. I would go even further. Although technically a vector of references may result in undefined behavior, I don't think that a standard-conforming compiler and library could even compile a program purporting to include such a constuct, because it would involve a reference to a reference. At any rate, I tried it on three compilers, and all choked. The standard says it's undefined behavior. So an implementation is free to make it work, or make it do anything else. By means of partial specialization, other meta-programming techiques, or even compiler magic. So while I suspect that in practice, you normally will get a compiler error, formally, it's still undefined behavior. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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