C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Multidimensional arrays as function arguments          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Ron Guest Posted: Fri Dec 12, 2003 9:46 am    Post subject: Multidimensional arrays as function arguments I have some legacy code that uses multidimensional arrays, which I need to pass to various functions* I'd like to pass them as const arguments to make it clear that these function shouldn't modify them. I know how this works for 2d arrays (s.4.4(4)): char *someArray[20]; ... void f (const char * const *a, int missingDimSize) {...} ... f (someArray, 20); However, I haven't been able to come up with the right list of const qualifiers to make it work with 3d arrays: char *someArray[20][30]; ... void f (const char * const (* a) [30], int missingDimSize); // ??? ... f (someArray, 20); // compiler says "incompatible pointer types" * I wish I could change this code to use nested std::vector <>s, but no dice. [ 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: Fri Dec 12, 2003 6:28 pm    Post subject: Re: Multidimensional arrays as function arguments In article <c668c1f8.0312111557.6840a742 (AT) posting (DOT) google.com>, Ron <rcrane (AT) ictv (DOT) com> writes Quote: I have some legacy code that uses multidimensional arrays, which I need to pass to various functions* I'd like to pass them as const arguments to make it clear that these function shouldn't modify them. I know how this works for 2d arrays (s.4.4(4)): consider: int const dim1(30); int const dim2(40); int const dim3(5); typedef int array3d[dim1][dim2][dim3]; void foo(array3d const &); In C++ we can pass arrays around by reference provided we have fixed dimensions. You could even use a function template: #include <iostream> template<int d1, int d2, int d3> void foo(int const ( &ar )[d1][d2][d3]){std::cout << ar[0][0][0];} int main(){ int a[3][4][5] = {1,2,3}; foo<3,4,5>(a); } However watch out for code bloat. -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit or http://www.robinton.demon.co.uk [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Bogdan Guest Posted: Sat Dec 13, 2003 2:12 am    Post subject: Re: Multidimensional arrays as function arguments [email]rcrane (AT) ictv (DOT) com[/email] (Ron) wrote in message news:<c668c1f8.0312111557.6840a742 (AT) posting (DOT) google.com>... Quote: I have some legacy code that uses multidimensional arrays, which I need to pass to various functions* I'd like to pass them as const arguments to make it clear that these function shouldn't modify them. I know how this works for 2d arrays (s.4.4(4)): char *someArray[20]; ... void f (const char * const *a, int missingDimSize) {...} ... f (someArray, 20); However, I haven't been able to come up with the right list of const qualifiers to make it work with 3d arrays: char *someArray[20][30]; ... void f (const char * const (* a) [30], int missingDimSize); // ??? ... f (someArray, 20); // compiler says "incompatible pointer types" * I wish I could change this code to use nested std::vector <>s, but no dice. Hi, VC++6 says: "Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast" Try this: f( (const char * const (*)[30])someArray, 20 ); Regards, Bogdan [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ron Guest Posted: Sat Dec 13, 2003 11:23 am    Post subject: Re: Multidimensional arrays as function arguments Quote: I have some legacy code that uses multidimensional arrays, which I need to pass to various functions* I'd like to pass them as const arguments to make it clear that these function shouldn't modify them. I know how this works for 2d arrays (s.4.4(4)): consider: int const dim1(30); int const dim2(40); int const dim3(5); typedef int array3d[dim1][dim2][dim3]; void foo(array3d const &); In C++ we can pass arrays around by reference provided we have fixed dimensions.... Hmm, that sounds good. But is there any way to do it without using references, as with code that needs also to be compilable with a "C" compiler? -Ron [ 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: Sat Dec 13, 2003 3:41 pm    Post subject: Re: Multidimensional arrays as function arguments In article <c668c1f8.0312122328.18c472de (AT) posting (DOT) google.com>, Ron <rcrane (AT) ictv (DOT) com> writes Quote: I have some legacy code that uses multidimensional arrays, which I need to pass to various functions* I'd like to pass them as const arguments to make it clear that these function shouldn't modify them. I know how this works for 2d arrays (s.4.4(4)): consider: int const dim1(30); int const dim2(40); int const dim3(5); typedef int array3d[dim1][dim2][dim3]; void foo(array3d const &); In C++ we can pass arrays around by reference provided we have fixed dimensions.... Hmm, that sounds good. But is there any way to do it without using references, as with code that needs also to be compilable with a "C" compiler? Of course, and very simply: void foo(array3d const * const); The only other change is that my declarations of dim1, dim2 and dim3 become either #defines or: enum dimensions{first = 30, second = 40, third = 5}; For reasons of portability while retaining at least a semblance of scope sensitivity I prefer the latter. -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit or http://www.robinton.demon.co.uk [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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