Question

I have a need to be able to have a super class execute callbacks defined by a class that inherits from it. I am relatively new to C++ and from what I can tell it looks like the subject of member-function-pointers is a very murky area.

I have seen answers to questions and random blog posts that discuss all sorts of things, but I am not sure if any of them are specifically dealing with my question here.

Here is a simple chunk of code that illustrates what I am trying to do. The example might not make a lot of sense, but it accurately resembles the code I am trying to write.

class A {     protected:     void doSomething(void (A::*someCallback)(int a)) {         (*this.*someCallback)(1234);     } };  class B : public A {     public:     void runDoIt() { doSomething(&B::doIt); }     void runDoSomethingElse() { doSomething(&B::doSomethingElse); }     protected:     void doIt(int foo) {         cout << 'Do It! [' << foo << ']\n';     }     void doSomethingElse(int foo) {         cout << 'Do Something Else! [' << foo << ']\n';     } };  int main(int argc, char *argv[]) {     B b;     b.runDoIt();     b.runDoSomethingElse(); } 

Answer 1

If you can use boost libraries, I would suggest you use boost::function for the task at hand.

class A { public:    void doSomething( boost::function< void ( int ) > callback )    {       callback( 5 );    } }; 

Then any inheriting (or external class) can use boost::bind do make a call:

class B { public:    void my_method( int a ); }; void test() {    B b;    A a;    a.doSomething( boost::bind( &B::my_method, &b, _1 ) ); }; 

I have not checked the exact syntax and I have typed it from the top of my head, but that is at least close to the proper code.