C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Re: valarray resize          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Harald Grossauer Guest Posted: Mon Jul 28, 2003 12:42 pm    Post subject: Re: valarray resize Marc Schellens wrote: Quote: I learned (the hard way) that a valarray does not copy its elements upont relocation when resize() is used. At least for gcc 3.2 this is true. Is that standard conform? Yes. Quote: And: If I make the valarray smaller with resize(), can I be sure that at least then no data is lost? No. Quote: thanks, marc Back to top Marc Schellens Guest Posted: Tue Jul 29, 2003 6:24 am    Post subject: Re: valarray resize Quote: Marc Schellens wrote: I learned (the hard way) that a valarray does not copy its elements upon relocation when resize() is used. Is that standard conform? Yes. And: If I make the valarray smaller with resize(), can I be sure that at least then no data is lost? No. In fact, it will almost certainly be lost. A valarray is a *rigid* array [of numbers]. You aren't supposed to resize a valarray except in very special circumstances. For example, suppose that you want to create an array of valarray's valarray<double> A[m]; // m is a positive constant The C++ compiler calls the default constructor to initialize each of the m valarray's then you can use the resize operator to give each valarray its appropriate size. If you find that you need to resize a valarray that you have already initialized consider the possibility that you may have chosen the wrong type of container. Consider, for example, vector class templates instead. A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r r is equal size OR SMALLER than l. Can I say in the latter case: l=pow( l, r); If not, any suggestions? thanks, marc Back to top Marc Schellens Guest Posted: Tue Jul 29, 2003 6:31 am    Post subject: Re: valarray resize Quote: A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r r is equal size OR SMALLER than l. Sorry, I meant: ... OR LARGER ... Quote: Can I say in the latter case: l=pow( l, r); If not, any suggestions? thanks, marc Back to top John Harrison Guest Posted: Tue Jul 29, 2003 6:39 am    Post subject: Re: valarray resize "Marc Schellens" <m_schellens (AT) hotmail (DOT) com> wrote Quote: A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r r is equal size OR SMALLER than l. Sorry, I meant: ... OR LARGER ... Can I say in the latter case: l=pow( l, r); If not, any suggestions? thanks, marc It would not be hard to use vectors, and write simple functions to perform the mathematical operations. john Back to top Marc Schellens Guest Posted: Tue Jul 29, 2003 1:58 pm    Post subject: Re: valarray resize Quote: "Marc Schellens" <m_schellens (AT) hotmail (DOT) com> wrote in message news:3F2614DD.7030603 (AT) hotmail (DOT) com... A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r r is equal size OR SMALLER than l. Sorry, I meant: ... OR LARGER ... Can I say in the latter case: l=pow( l, r); If not, any suggestions? thanks, marc It would not be hard to use vectors, and write simple functions to perform the mathematical operations. So does this mean, that for any function both valarray operands must have the same size? Of course I could write simple functions, but on the other hand, exactly that is what valarrays are for, isn't it? The performance might be also much better with valarrays. Apart from that I don't see any reason why a valarray should loose its contents when shrinking. Why is this (or can be) so? thanks, marc Back to top E. Robert Tisdale Guest Posted: Tue Jul 29, 2003 3:00 pm    Post subject: Re: valarray resize Marc Schellens wrote: Quote: A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r where l.size() <= r.size(). r is equal size OR SMALLER than l. Can I say in the latter case: l = pow(l, r); If not, any suggestions? First, you need to tell us what you mean by pow(l, r). Back to top Marc Schellens Guest Posted: Wed Jul 30, 2003 7:06 am    Post subject: Re: valarray resize E. Robert Tisdale wrote: Quote: Marc Schellens wrote: A valarray is conveninet for me because of the mathematical operaions. I have two valarray<double>, l and r where l.size() <= r.size(). r is equal size OR SMALLER than l. Can I say in the latter case: l = pow(l, r); If not, any suggestions? First, you need to tell us what you mean by pow(l, r). I meant the valarray pow function: template valarray<Ty> pow(const valarray<Ty>& left, const valarray<Ty>& right); but this was just an example. Basically my question was about all arithmetic valarray functions. thanks, marc 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.