C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  valarray, why no begin() / end()?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message christopher diggins Guest Posted: Sat Jun 04, 2005 2:27 am    Post subject: valarray, why no begin() / end()? Does any one know why there is no begin() / end() functions for valarray? -- Christopher Diggins http://www.cdiggins.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Sat Jun 04, 2005 12:25 pm    Post subject: Re: valarray, why no begin() / end()? "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: Quote: Does any one know why there is no begin() / end() functions for valarray? Because they are thought of as "whole thingy" collections rather than sequences. You might argue that associative containers are not sequences, but the difference here is that, fundamentally valarrays are supposed to support single instruction multiple data (SIMD) operations and being free of some form of alias. In such a perspective, begin() and end() operations are barrely relevant. -- Gabriel Dos Reis [email]gdr (AT) integrable-solutions (DOT) net[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top christopher diggins Guest Posted: Sat Jun 04, 2005 6:14 pm    Post subject: Re: valarray, why no begin() / end()? "Gabriel Dos Reis" <gdr (AT) integrable-solutions (DOT) net> wrote Quote: "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: | Does any one know why there is no begin() / end() functions for valarray? Because they are thought of as "whole thingy" collections rather than sequences. You might argue that associative containers are not sequences, but the difference here is that, fundamentally valarrays are supposed to support single instruction multiple data (SIMD) operations and being free of some form of alias. In such a perspective, begin() and end() operations are barrely relevant. Does this mean then that usage such as: std::valarray<int> v(10); int* first = &v[0]; int* end = &v[v.size()]; is not recommned because it creates an alias? Thank you for your help! -Christopher Diggins [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Sun Jun 05, 2005 9:30 am    Post subject: Re: valarray, why no begin() / end()? "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: Quote: "Gabriel Dos Reis" <gdr (AT) integrable-solutions (DOT) net> wrote in message news:m3d5r2hf2t.fsf (AT) uniton (DOT) integrable-solutions.net... "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: | Does any one know why there is no begin() / end() functions for valarray? Because they are thought of as "whole thingy" collections rather than sequences. You might argue that associative containers are not sequences, but the difference here is that, fundamentally valarrays are supposed to support single instruction multiple data (SIMD) operations and being free of some form of alias. In such a perspective, begin() and end() operations are barrely relevant. Does this mean then that usage such as: std::valarray<int> v(10); int* first = &v[0]; int* end = &v[v.size()]; ^^^^^^^^^^^^ Parenthetical note: I think you wanted to say &v[0] + v.size(); Quote: is not recommned because it creates an alias? You can create pointers into valarray<>s as long as you obey other C++ rules, it is just that they are not thought of actively supporting aliasing. -- Gabriel Dos Reis [email]gdr (AT) integrable-solutions (DOT) net[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jerry Coffin Guest Posted: Mon Jun 06, 2005 7:25 am    Post subject: Re: valarray, why no begin() / end()? In article <hO2oe.28092$3N5.594359 (AT) weber (DOT) videotron.net>, [email]cdiggins (AT) videotron (DOT) ca[/email] says... Quote: Does any one know why there is no begin() / end() functions for valarray? Because valarray is not a container, in the usual sense of the word. The primary idea of valarray was to provide something that was sufficiently restricted to allow optimizations that were considered impossible (or at least unlikely) with general containers. -- Later, Jerry. The universe is a figment of its own imagination. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Clark S. Cox III Guest Posted: Fri Jun 10, 2005 10:18 am    Post subject: Re: valarray, why no begin() / end()? On 2005-06-05 05:30:45 -0400, Gabriel Dos Reis <gdr (AT) integrable-solutions (DOT) net> said: Quote: "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: | "Gabriel Dos Reis" <gdr (AT) integrable-solutions (DOT) net> wrote in message | news:m3d5r2hf2t.fsf (AT) uniton (DOT) integrable-solutions.net... | > "christopher diggins" <cdiggins (AT) videotron (DOT) ca> writes: | | > | Does any one know why there is no begin() / end() functions for | > valarray? | | > Because they are thought of as "whole thingy" collections rather than | > sequences. | > You might argue that associative containers are not sequences, but the | > difference here is that, fundamentally valarrays are supposed to | > support single instruction multiple data (SIMD) operations and being | > free of some form of alias. | > In such a perspective, begin() and end() operations are barrely | > relevant. | | Does this mean then that usage such as: | | std::valarray<int> v(10); | int* first = &v[0]; | int* end = &v[v.size()]; ^^^^^^^^^^^^ Parenthetical note: I think you wanted to say &v[0] + v.size(); And the difference is? #include <valarray> #include <iostream> using namespace std; int main() { valarray<int> arr(20); for(size_t i=0; i { cout << boolalpha << (&arr[i] == &arr[0] + i) << endl; } return 0; } -- Clark S. Cox, III [email]clarkcox3 (AT) gmail (DOT) com[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Fri Jun 10, 2005 4:32 pm    Post subject: Re: valarray, why no begin() / end()? "Clark S. Cox III" <clarkcox3 (AT) gmail (DOT) com> writes: [...] Quote: | Does this mean then that usage such as: | | std::valarray<int> v(10); | int* first = &v[0]; | int* end = &v[v.size()]; ^^^^^^^^^^^^ Parenthetical note: I think you wanted to say &v[0] + v.size(); And the difference is? there is no element at v.size() whose address is being taken. -- Gabriel Dos Reis [email]gdr (AT) integrable-solutions (DOT) net[/email] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maciej Sobczak Guest Posted: Fri Jun 10, 2005 4:33 pm    Post subject: Re: valarray, why no begin() / end()? Hi, Clark S. Cox III wrote: Quote: | int* end = &v[v.size()]; ^^^^^^^^^^^^ Parenthetical note: I think you wanted to say &v[0] + v.size(); And the difference is? The difference is that v[v.size()] is already undefined behaviour. You can reach past-the-end pointer (with pointer arithmetic), but you cannot take the address of past-the-end element. There is no such element. On popular platforms it might not be a problem, though. -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/ [ 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.