How do I implement a callback in C++?

Question

I want to implement a class in c++ that has a callback.

So I think I need a method that has 2 arguments:

the target object. (let's say *myObj)
the pointer to a member function of the target object. (so i can do *myObj->memberFunc(); )

The conditions are:

myObj can be from any class.
the member function that is gonna be the callback function is non-static.

I've been reading about this but it seems like I need to know the class of myObj before hand. But I am not sure how to do it. How can I handle this? Is this possible in C++?

This is something I have in mind but is surely incorrect.

class MyClassWithCallback{
public
    void *targetObj;
    void (*callback)(int number);
    void setCallback(void *myObj, void(*callbackPtr)(int number)){
        targetObj = myObj;
        callback = callbackPtr;
    };
    void callCallback(int a){
        (myObj)->ptr(a);
    };
};
class Target{
public
    int res;
    void doSomething(int a){//so something here. This is gonna be the callback function};        
};

int main(){
    Target myTarget;
    MyClassWithCallback myCaller;
    myCaller.setCallback((void *)&myTarget, &doSomething);

}

I appreciate any help.

Thank you.

UPDATE Most of you said Observing and Delegation, well that's i exactly what i am looking for, I am kind of a Objective-C/Cocoa minded guy. My current implementation is using interfaces with virtual functions. Is just I thought it would be "smarter" to just pass the object and a member function pointer (like boost!) instead of defining an Interface. But It seems that everybody agrees that Interfaces are the easiest way right? Boost seems to be a good idea, (assuming is installed)

How do I implement a callback in C++?

6 Answers