C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Returning NULL references...          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Tony Di Croce Guest Posted: Wed Sep 29, 2004 3:56 pm    Post subject: Returning NULL references... Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Tony Back to top Moonlit Guest Posted: Wed Sep 29, 2004 4:02 pm    Post subject: Re: Returning NULL references... Hi, "Tony Di Croce" <dicroce (AT) gmail (DOT) com> wrote Quote: Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Yes, it creates an entry to the map and returns a reference to it (that's why [] isn't constant). Quote: Tony Do the same as the STL or throw an exception or return a reference to for instance a local (to the class) variable. Of course just adding an entry will keep yourself and people reading your code, from any surprises since that is what people expect. Regards, Ron AF Greve. Back to top Andre Kostur Guest Posted: Wed Sep 29, 2004 4:03 pm    Post subject: Re: Returning NULL references... [email]dicroce (AT) gmail (DOT) com[/email] (Tony Di Croce) wrote in news:37c0928e.0409290756.721f58d8 (AT) posting (DOT) google.com: Quote: Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? An exception. Or leave it as undefined behaviour. Quote: This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Undefined behaviour. One of the strong points of references is that they _cannot_ be "NULL" (at least not without invoking undefined behaviour). Back to top Peter Koch Larsen Guest Posted: Wed Sep 29, 2004 4:04 pm    Post subject: Re: Returning NULL references... "Tony Di Croce" <dicroce (AT) gmail (DOT) com> skrev i en meddelelse news:37c0928e.0409290756.721f58d8 (AT) posting (DOT) google.com... Quote: Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? Is it something like a std::vector? In that case, i would terminate the program or possibly throw - but that is a design decision, of course. Quote: This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Sounds strange! Most of the time i return references, i will have a variable to return. Quote: Does anyone know what does the STL does? For a set, the element is created with the value T(). For a std::vector, behaviour is undefined - an implementation can do what it likes. Quote: Tony /Peter Back to top Andre Kostur Guest Posted: Wed Sep 29, 2004 4:12 pm    Post subject: Re: Returning NULL references... Andre Kostur <nntpspam (AT) kostur (DOT) net> wrote in news:Xns95735C19ECCECnntpspamkosturnet (AT) 207 (DOT) 35.177.134: Quote: dicroce (AT) gmail (DOT) com (Tony Di Croce) wrote in news:37c0928e.0409290756.721f58d8 (AT) posting (DOT) google.com: Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? An exception. Or leave it as undefined behaviour. This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Undefined behaviour. One of the strong points of references is that they _cannot_ be "NULL" (at least not without invoking undefined behaviour). Oops.. I'm thinking specifically of vectors. For map and set that would create a default-constructed object at that index and return a reference to that.... Back to top Maitre Bart Guest Posted: Wed Sep 29, 2004 5:53 pm    Post subject: Re: Returning NULL references... "Andre Kostur" <nntpspam (AT) kostur (DOT) net> wrote Quote: Andre Kostur <nntpspam (AT) kostur (DOT) net> wrote in news:Xns95735C19ECCECnntpspamkosturnet (AT) 207 (DOT) 35.177.134: [email]dicroce (AT) gmail (DOT) com[/email] (Tony Di Croce) wrote in news:37c0928e.0409290756.721f58d8 (AT) posting (DOT) google.com: Given: T& operator [] ( int index ); // T is a parameterized type What should be returned when index is out of range? An exception. Or leave it as undefined behaviour. This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Undefined behaviour. One of the strong points of references is that they _cannot_ be "NULL" (at least not without invoking undefined behaviour). Oops.. I'm thinking specifically of vectors. For map and set that would create a default-constructed object at that index and return a reference to that.... You may as well increase your vector size up to the specified index. That way you would get about the same behavior you just described for map and set. Anyway, if the vector is not able to allocate, it will result in an axception of some sort. So better be prepared for an exception anyway. Back to top Andre Kostur Guest Posted: Wed Sep 29, 2004 7:08 pm    Post subject: Re: Returning NULL references... "Maitre Bart" <lemieux (AT) cae (DOT) com> wrote in news:cjesqn$9ac$1 (AT) dns3 (DOT) cae.ca: Quote: This same question comes up virtually everywhere I return a reference. I need to return a reference (as opposed to a copy) because I want to use this operator as an l-value sometimes... Does anyone know what does the STL does? Undefined behaviour. One of the strong points of references is that they _cannot_ be "NULL" (at least not without invoking undefined behaviour). Oops.. I'm thinking specifically of vectors. For map and set that would create a default-constructed object at that index and return a reference to that.... You may as well increase your vector size up to the specified index. Up to what size? You may not know the maximum index before you start. As a result, you'll have to pay for the construction of all of these extra objects that you may not ever use.... Quote: That way you would get about the same behavior you just described for map and set. Not really. With map and set, you won't have a bunch of extra objects being constructed just in case... Quote: Anyway, if the vector is not able to allocate, it will result in an axception of some sort. So better be prepared for an exception anyway. 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 (comp.lang.c++) 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.