C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  help : how to : array of method pointers          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message max reason Guest Posted: Wed Jan 28, 2004 11:41 am    Post subject: help : how to : array of method pointers A method in one of my classes needs to call one of 256 other methods in the same class based on an unsigned 8-bit value (0x00 to 0xFF). How is this done? Everything I try generates errors. Something this basic can't be so difficult (or impossible) - can it? Thanks. The following roughly shows what I want: class simple { public: simple(); // constructor ~simple(); // destructor int process(); // public method private: simple* process_0x00 (int* value); simple* process_0x01 (int* value); simple* process_0x02 (int* value); // declare rest of the 256 methods here simple* process_0xFE (int* value); simple* process_0xFF (int* value); // // now, declare 256 element array to hold addresses of 256 methods ( process_0x00() to process_0xFF() ) // static simple* (simple::*dispatch[0x0100])(int* value); // all methods have identical return & argument types }; // // then, in the simple.cpp file // // write the 256 methods // simple* simple::process_0x00 (int* value) { // do something } simple* simple::process_0x01 (int* value) { // do something } simple* simple::process_0x02 (int* value) { // do something } // define rest of the 256 methods here simple* simple::process_0xFE (int* value) { // do something } simple* simple::process_0xFF (int* value) { // do something } // // fill the 256-element method-pointer array with method addresses // simple* ((uniform::*process[256])(int*)) = { &simple::process_0x00(int*), &simple::process_0x01(int*), &simple::process_0x02(int*), // fill rest of the 256 element method-pointer array here &simple::process_0xFD(int*), &simple::process_0xFE(int*), &simple::process_0xFF(int*), }; // // method that calls one of 256 methods in the method pointer array // int process (int value) { simple* result = uniform::dispatch[value](&value); } It oughta be simple, right? It is easy in C - why not with C++ ??? HELP - thanks in advance Back to top Peter Koch Larsen Guest Posted: Wed Jan 28, 2004 12:21 pm    Post subject: Re: help : how to : array of method pointers "max reason" <maxreason (AT) NOSPAMmaxreason (DOT) com> skrev i en meddelelse news:101f7omqmr0a663 (AT) corp (DOT) supernews.com... Quote: A method in one of my classes needs to call one of 256 other methods in the same class based on an unsigned 8-bit value (0x00 to 0xFF). How is this done? Everything I try generates errors. Something this basic can't be so difficult (or impossible) - can it? Thanks. The following roughly shows what I want: class simple { public: simple(); // constructor ~simple(); // destructor int process(); // public method private: simple* process_0x00 (int* value); simple* process_0x01 (int* value); simple* process_0x02 (int* value); // declare rest of the 256 methods here simple* process_0xFE (int* value); simple* process_0xFF (int* value); // // now, declare 256 element array to hold addresses of 256 methods ( process_0x00() to process_0xFF() ) // static simple* (simple::*dispatch[0x0100])(int* value); // all methods have identical return & argument types }; // // then, in the simple.cpp file // // write the 256 methods // simple* simple::process_0x00 (int* value) { // do something } simple* simple::process_0x01 (int* value) { // do something } simple* simple::process_0x02 (int* value) { // do something } // define rest of the 256 methods here simple* simple::process_0xFE (int* value) { // do something } simple* simple::process_0xFF (int* value) { // do something } // // fill the 256-element method-pointer array with method addresses // simple* ((uniform::*process[256])(int*)) = { What is uniform??? [snip] Quote: }; // // method that calls one of 256 methods in the method pointer array // int process (int value) { simple* result = uniform::dispatch[value](&value); You must provide an object to call with. Quote: } It oughta be simple, right? It is easy in C - why not with C++ ??? HELP - thanks in advance Well... a typedef might make it simpler, perhaps? class simple {...}; typedef simple* (simple::*simple_functor)(int *value); simple_functor dispatch[256] = { simple::process_0x00, simple::process_0x01, ..... simple::process_0xFF, } Now call it like this: simple s1; int i; simple *result = (s1.*dispatch[0x67])(&i); A little bit complicated, that pointer-to-memberfunction syntax, but perhaps I have not understood your question? /Peter Back to top Peter Koch Larsen Guest Posted: Wed Jan 28, 2004 12:26 pm    Post subject: Re: help : how to : array of method pointers "Peter Koch Larsen" <pklspam (AT) mailme (DOT) dk> skrev i en meddelelse news:aPNRb.80002$jf4.5147421 (AT) news000 (DOT) worldonline.dk... Quote: simple_functor dispatch[256] = { simple::process_0x00, simple::process_0x01, Missing ampersand. Should be (for all functions): &simple::process_0x01, Quote: .... simple::process_0xFF, } The code in my original reply is not tested. One fault is above - but there may be others. Back to top Rob Williscroft Guest Posted: Wed Jan 28, 2004 12:30 pm    Post subject: Re: help : how to : array of method pointers max reason wrote in news:101f7omqmr0a663 (AT) corp (DOT) supernews.com: Quote: A method in one of my classes needs to call one of 256 other methods in the same class based on an unsigned 8-bit value (0x00 to 0xFF). How is this done? Everything I try generates errors. Something this basic can't be so difficult (or impossible) - can it? Thanks. The following roughly shows what I want: [snip] #include <iostream> class simple { public: int process( int value ); private: simple* process_0x00 (int* value); simple* process_0x01 (int* value); simple* process_0x02 (int* value); static simple* (simple::*dispatch[3])(int* value); }; simple* simple::process_0x00 (int* value) { std::cerr << "0: " << *value << 'n'; return this; } simple* simple::process_0x01 (int* value) { std::cerr << "1: " << *value << 'n'; return this; } simple* simple::process_0x02 (int* value) { std::cerr << "2: " << *value << 'n'; return this; } /* Note the extra "simple" */ simple* (simple::*simple::dispatch[3])(int*) = { &simple::process_0x00, &simple::process_0x01, &simple::process_0x02, }; int simple::process(int value) { /* how to call a member pointer */ (this->*dispatch[value])(&value); return value; } int main() { simple s; for ( int i = 0; i < 3; ++i ) s.process( i ); } Quote: It oughta be simple, right? It is easy in C - why not with C++ ??? HELP - thanks in advance Rob. -- http://www.victim-prime.dsl.pipex.com/ Back to top Karl Heinz Buchegger Guest Posted: Wed Jan 28, 2004 1:39 pm    Post subject: Re: help : how to : array of method pointers max reason wrote: Quote: A method in one of my classes needs to call one of 256 other methods in the same class based on an unsigned 8-bit value (0x00 to 0xFF). How is this done? Everything I try generates errors. Which errors? Quote: It oughta be simple, right? It is easy in C - why not with C++ ??? It is easy with C++ too. You just need to get the syntax right. In the future please dont' post roughly the code you have but post the real code you have and add the error message. This will help us because * we don't have to wade through lots of code just to find the spot which causes you troubles. * we don't fix bugs that are not there in your real code. This compiles without problems. class simple; typedef simple* ( simple::*FnctPtr )( int* value ); class simple { public: simple(); // constructor ~simple(); // destructor int process( int ); // public method public: simple* process_0x00 (int* value); simple* process_0x01 (int* value); simple* process_0x02 (int* value); // declare rest of the 256 methods here simple* process_0xFE (int* value); simple* process_0xFF (int* value); // // now, declare 256 element array to hold addresses of 256 methods ( process_0x00() to process_0xFF() ) // static FnctPtr dispatch[0x100]; // all methods have identical return & argument types }; // // then, in the simple.cpp file // // write the 256 methods // simple* simple::process_0x00 (int* value) { /* do something */ return 0; } simple* simple::process_0x01 (int* value) { /* do something */ return 0; } simple* simple::process_0x02 (int* value) { /* do something */ return 0; } // define rest of the 256 methods here simple* simple::process_0xFE (int* value) { /* do something */ return 0; } simple* simple::process_0xFF (int* value) { /* do something */ return 0; } // // fill the 256-element method-pointer array with method addresses // FnctPtr simple::dispatch[] = { simple::process_0x00, simple::process_0x01, simple::process_0x02, // fill rest of the 256 element method-pointer array here simple::process_0xFE, simple::process_0xFF, }; // // method that calls one of 256 methods in the method pointer array // int simple::process (int value) { simple* result = (this->*dispatch[value])(&value); return 0; } -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top David Harmon Guest Posted: Wed Jan 28, 2004 2:59 pm    Post subject: Re: help : how to : array of method pointers On Wed, 28 Jan 2004 14:39:04 +0100 in comp.lang.c++, Karl Heinz Buchegger <kbuchegg (AT) gascad (DOT) at> was alleged to have written: Quote: class simple; typedef simple* ( simple::*FnctPtr )( int* value ); class simple { Is there a reason you went to extra trouble to put the typedef outside the class definition, rather than putting it inside and thus making it private to the class? Back to top Karl Heinz Buchegger Guest Posted: Wed Jan 28, 2004 3:37 pm    Post subject: Re: help : how to : array of method pointers David Harmon wrote: Quote: On Wed, 28 Jan 2004 14:39:04 +0100 in comp.lang.c++, Karl Heinz Buchegger <kbuchegg (AT) gascad (DOT) at> was alleged to have written: class simple; typedef simple* ( simple::*FnctPtr )( int* value ); class simple { Is there a reason you went to extra trouble to put the typedef outside the class definition, rather than putting it inside and thus making it private to the class? No. No real reason. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top max reason Guest Posted: Thu Jan 29, 2004 12:23 am    Post subject: Re: help : how to : array of method pointers Thanks for pointing out the errors in my question. The following is the fixed question - the question I actually want answered! A method in one of my classes needs to call one of 256 other methods in the same class based on an unsigned 8-bit value (0x00 to 0xFF). How is this done? Everything I try generates errors. Something this basic can't be so difficult (or impossible) - can it? Thanks. The following roughly shows what I want: class simple { public: simple(); // constructor ~simple(); // destructor int process(); // public method private: simple* process_0x00 (int* value); simple* process_0x01 (int* value); simple* process_0x02 (int* value); // declare rest of the 256 methods here simple* process_0xFE (int* value); simple* process_0xFF (int* value); // // now, declare 256 element array to hold addresses of 256 methods ( process_0x00() to process_0xFF() ) // static simple* (simple::*dispatch[0x0100])(int* value); // all methods have identical return & argument types }; // // then, in the simple.cpp file // // write the 256 methods // simple* simple::process_0x00 (int* value) { // do something } simple* simple::process_0x01 (int* value) { // do something } simple* simple::process_0x02 (int* value) { // do something } // define rest of the 256 methods here simple* simple::process_0xFE (int* value) { // do something } simple* simple::process_0xFF (int* value) { // do something } // // fill the 256-element method-pointer array with method addresses // simple* ((simple::*process[256])(int*)) = { &simple::process_0x00(int*), &simple::process_0x01(int*), &simple::process_0x02(int*), // fill rest of the 256 element method-pointer array here &simple::process_0xFD(int*), &simple::process_0xFE(int*), &simple::process_0xFF(int*), }; // // method that calls one of 256 methods in the method pointer array // int process (int value) { simple* result = simple::dispatch[value](&value); } It oughta be simple, right? It is easy in C - why not with C++ ??? HELP - thanks in advance 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.