C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  overloading [] operator for matrix?          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Dave Guest Posted: Sat Feb 28, 2004 5:08 am    Post subject: overloading [] operator for matrix? Hi there: i am doing a matrix class for practice. everything is ok except the [] operator. Basically, i want to achieve the same way as the normal double[]'s, such as: m[2][3] = 4.0; m[3][4] = m[4][5] + m[2][3]; cout< I also want the indices to be 1 based instead of 0 based. One way I can think out is to have the following overloaded operator in matrix class: double* operator [] (int row_index); suppose the matrix contains doubles and i am using a double pointer to store the numbers. but I have the following problems with this approach: 1. the second index can't be 1 based since it's used to directly indexed into the double*. It has to be 0 based. 2. it's not safe. since the function returns the row pointer. the caller can just call m[2] and then do some bad things. but that's the only way I can think out now. Is there a good way to solve this problem? Thanks a lot. Back to top Victor Bazarov Guest Posted: Sat Feb 28, 2004 5:32 am    Post subject: Re: overloading [] operator for matrix? "Dave" <davis_eric (AT) yahoo (DOT) com> wrote... Quote: i am doing a matrix class for practice. everything is ok except the [] operator. Basically, i want to achieve the same way as the normal double[]'s, such as: m[2][3] = 4.0; m[3][4] = m[4][5] + m[2][3]; cout< I also want the indices to be 1 based instead of 0 based. One way I can think out is to have the following overloaded operator in matrix class: double* operator [] (int row_index); suppose the matrix contains doubles and i am using a double pointer to store the numbers. but I have the following problems with this approach: 1. the second index can't be 1 based since it's used to directly indexed into the double*. It has to be 0 based. 2. it's not safe. since the function returns the row pointer. the caller can just call m[2] and then do some bad things. but that's the only way I can think out now. Is there a good way to solve this problem? A good way to solve it is to have a special proxy class, which in turn will have double& operator[](int column) implemented with your rules. Make that class a member of your matrix class. Victor Back to top Cy Edmunds Guest Posted: Sat Feb 28, 2004 5:45 am    Post subject: Re: overloading [] operator for matrix? "Dave" <davis_eric (AT) yahoo (DOT) com> wrote Quote: Hi there: i am doing a matrix class for practice. everything is ok except the [] operator. Basically, i want to achieve the same way as the normal double[]'s, such as: m[2][3] = 4.0; m[3][4] = m[4][5] + m[2][3]; cout< I also want the indices to be 1 based instead of 0 based. One way I can think out is to have the following overloaded operator in matrix class: double* operator [] (int row_index); suppose the matrix contains doubles and i am using a double pointer to store the numbers. but I have the following problems with this approach: 1. the second index can't be 1 based since it's used to directly indexed into the double*. It has to be 0 based. Why? Can't you make the pointer point one location before the actual data? We did it for years in Fortran. Of course there is some inefficiency with computing the offset, but that's 1-based indexing for you. Quote: 2. it's not safe. since the function returns the row pointer. the caller can just call m[2] and then do some bad things. Don't look now but indexing isn't safe. It's just pointer arithmetic in disguise. Quote: but that's the only way I can think out now. Is there a good way to solve this problem? You could have your operator [] return a "row" class representing a row in your matrix. There might be some advantage to this for implementing operations such as row swapping. However it's not going to be more efficient for indexing than just returning a pointer and may be considerably less so. Quote: Thanks a lot. -- Cy http://home.rochester.rr.com/cyhome/ Back to top John Harrison Guest Posted: Sat Feb 28, 2004 7:22 am    Post subject: Re: overloading [] operator for matrix? "Dave" <davis_eric (AT) yahoo (DOT) com> wrote Quote: Hi there: i am doing a matrix class for practice. everything is ok except the [] operator. Basically, i want to achieve the same way as the normal double[]'s, such as: m[2][3] = 4.0; m[3][4] = m[4][5] + m[2][3]; cout< I also want the indices to be 1 based instead of 0 based. One way I can think out is to have the following overloaded operator in matrix class: double* operator [] (int row_index); suppose the matrix contains doubles and i am using a double pointer to store the numbers. but I have the following problems with this approach: 1. the second index can't be 1 based since it's used to directly indexed into the double*. It has to be 0 based. 2. it's not safe. since the function returns the row pointer. the caller can just call m[2] and then do some bad things. but that's the only way I can think out now. Is there a good way to solve this problem? Yes, this gets asked quite a lot. Search this group for "proxy class". john 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.