C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  large arrays versus standard containers          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Pierre Espenan Guest Posted: Mon Dec 29, 2003 10:58 am    Post subject: large arrays versus standard containers In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Tue Dec 30, 2003 12:50 am    Post subject: Re: large arrays versus standard containers In message <UNJHb.22980$Pg1.11239 (AT) newsread1 (DOT) news.pas.earthlink.net>, Pierre Espenan <whistling_rabbit (AT) yahoo (DOT) com> writes Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? Many systems have limited stack space and using a std::vector instead of a raw array ensures relatively low demand for stack space. OTOH there are reasons to go the other way, particularly for arrays of types that are not default initialised (if the programmer does not want time spent on immediate initialisation of all values). These days the difference in performance is usually small. Newcomers to programming have no need to learn about arrays until relatively late in the learning process because vector and string will meet their needs (well they would if only we could ensure that all the Standard Library functions that use char* were overloaded to accept std::string as well) -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit or http://www.robinton.demon.co.uk Happy Xmas, Hanukkah, Yuletide, Winter/Summer Solstice to all. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thorsten Ottosen Guest Posted: Tue Dec 30, 2003 12:50 am    Post subject: Re: large arrays versus standard containers "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> wrote Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? Yes. There is no reason to use builtin arrays. You can even use an array class template when you need a fixed sized array. Quote: If yes, what are the reasons for this preference? because C style arrays are very very error-prone to use and because std::vector is just as fast and because it is much much more handy. br Thorsten [ 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: Tue Dec 30, 2003 12:58 am    Post subject: Re: large arrays versus standard containers "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> writes: Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? In general, standard containers are preferred to arrays, regardless of size. One sometimes makes an exception for very small arrays which are themselves members of something which will be in a large array. But except when order of initialisation is an issue, that's about it. Quote: If yes, what are the reasons for this preference? The standard containers are first class objects, which work like everything else in the language. -- James Kanze mailto:kanze (AT) gabi-soft (DOT) fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 11 rue de Rambouillet, 78460 Chevreuse, France +33 1 41 89 80 93 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Peter Koch Larsen Guest Posted: Tue Dec 30, 2003 5:11 am    Post subject: Re: large arrays versus standard containers "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> skrev i en meddelelse news:UNJHb.22980$Pg1.11239 (AT) newsread1 (DOT) news.pas.earthlink.net... Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? I would actually prefer std:: containers in most situations, regardless of size. One exception could be when i need smaller, fixed-size vectors or if I want to avoid dynamic memory allocation. As to why, the answer lies in the added safety (when talking about vectors). Kind regards Peter Koch Larsen [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Wagner Bruna Guest Posted: Tue Dec 30, 2003 5:16 am    Post subject: Re: large arrays versus standard containers Hi, "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> wrote Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? This is discussed in the FAQ: http://www.parashift.com/c++-faq-lite/ But I'm not sure what do you mean by "large" arrays: are you referring to the common C practice of creating static sized arrays with "big enough" space? -- Wagner [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dhruv Guest Posted: Tue Dec 30, 2003 5:18 am    Post subject: Re: large arrays versus standard containers On Mon, 29 Dec 2003 05:58:42 -0500, Pierre Espenan wrote: Quote: In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? 1. The memory used in a large array is the maximum that you will even need to ensure no overflows, etc... while the memory reqd. for containers is approximately what is actully required. 2. Better cache efficiency (possibly)! 3. Accessor functions. 4. Possibly debugging facilities provided by the labrary provider. Regards, -Dhruv. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thorsten Ottosen Guest Posted: Tue Dec 30, 2003 12:41 pm    Post subject: Re: large arrays versus standard containers "Francis Glassborow" <francis (AT) robinton (DOT) demon.co.uk> wrote [snip] Quote: . OTOH there are reasons to go the other way, particularly for arrays of types that are not default initialised (if the programmer does not want time spent on immediate initialisation of all values). tr1::array<X,size> does not initialize values by default AFAIR. br Thorsten [ 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: Tue Dec 30, 2003 12:49 pm    Post subject: Re: large arrays versus standard containers "Peter Koch Larsen" <pkl (AT) mailme (DOT) dk> writes: Quote: "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> skrev i en meddelelse news:UNJHb.22980$Pg1.11239 (AT) newsread1 (DOT) news.pas.earthlink.net... In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? I would actually prefer std:: containers in most situations, regardless of size. One exception could be when i need smaller, fixed-size vectors or if I want to avoid dynamic memory allocation. More generally applicable, I think, is the order of initialization issue. Almost all of my C style arrays are of PODs, using {...} initialization with constant expressions. That way, I know that they will be initialized before any dynamic initialization starts. Quote: As to why, the answer lies in the added safety (when talking about vectors). Safety? Neither are really safe. Both allow verification. In practice, I think some implementations of std::vector do verify -- in the past I think there was also an implementation of C++ in which C style arrays were bounds checked (Centerline). But in practice, buffer overflow is a latent problem with both. I think that the real answer is first, that std::vector behaves like every other type in the system, with value semantics, and second, that it encompasses the size, which with C style arrays must be passed separately (and explicitely). The latter is a simple convenience; the former, on the other hand, makes reasoning about the code significantly simpler. -- James Kanze mailto:kanze (AT) gabi-soft (DOT) fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 11 rue de Rambouillet, 78460 Chevreuse, France +33 1 41 89 80 93 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Tue Dec 30, 2003 7:23 pm    Post subject: Re: large arrays versus standard containers In message <3ff10584$0$18693$afc38c87 (AT) news (DOT) optusnet.com.au>, Thorsten Ottosen <nesotto (AT) cs (DOT) auc.dk> writes Quote: "Francis Glassborow" <francis (AT) robinton (DOT) demon.co.uk> wrote in message news:8c8+BFBm1A8$EwDG (AT) robinton (DOT) demon.co.uk... [snip] . OTOH there are reasons to go the other way, particularly for arrays of types that are not default initialised (if the programmer does not want time spent on immediate initialisation of all values). tr1::array<X,size> does not initialize values by default AFAIR. The original question as I understood it concerned choosing between std::vector and raw C-style arrays. The UDT you reference is a wrapping of a raw array to make it more STL algorithm friendly. It provides a genuine choice where the stack usage becomes the major issue for sequences whose size is known at compile time. -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit or http://www.robinton.demon.co.uk Happy Xmas, Hanukkah, Yuletide, Winter/Summer Solstice to all. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Joe Gottman Guest Posted: Wed Dec 31, 2003 1:05 pm    Post subject: Re: large arrays versus standard containers "Peter Koch Larsen" <pkl (AT) mailme (DOT) dk> wrote Quote: "Pierre Espenan" <whistling_rabbit (AT) yahoo (DOT) com> skrev i en meddelelse news:UNJHb.22980$Pg1.11239 (AT) newsread1 (DOT) news.pas.earthlink.net... In general, is it true that standard containers, vectors etc. are preferred to large arrays? If yes, what are the reasons for this preference? I would actually prefer std:: containers in most situations, regardless of size. One exception could be when i need smaller, fixed-size vectors or if I want to avoid dynamic memory allocation. As to why, the answer lies in the added safety (when talking about vectors). Have you looked at the boost array class? (See [url]http://www.boost.org/libs/array/index.htm)[/url]. This is an STL compliant fixed-size array wrapper. Its as efficient as a C-style array, but it can be returned from a function or passed as a parameter to a function without suffering pointer-decay like an ordinary array. Joe Gottman [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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