Function pointers to pass on a method member

Question

Ok here is pseudo-code showing the problem. I want to pass on the Man's sayAh() method to the Dog instance.

class Man
{
public:
    void haveDogBiteYou(){
        Dog *mydog = new Dog();
        myDog->setCallback(&this->sayAh); // How???
        myDog->bite();
    }

    void sayAh(){
        cout << "AHHHHHH!";
    }
}



class Dog{
public:

    void (*callbackFunc)(void);

    void setCallback(void (*callbackFunc)(void)){
        this->callbackFunc=callbackFunc;
    }

    void bite(){
        callbackFunc();
    }

}

I'd like to have the code setup in a way that if I have another class like Kid (i.e., Man's subclass), I can pass on the callback to a method member of that function as well. So probably changing

void (*callbackFunc)(void);

to

void (Man::*callbackFunc)(void);

will not be an answer to this problem... By the way, I am open to other solutions... Something like Java's interface works great.

`void Man::sayAh()` should be static and you should delete `myDog` — Mohit Jain, May 09 '14 at 05:24
@MohitJain how will it solve his problem? How about using polymorphism? And have dog be aware of its master? — W.B., May 09 '14 at 05:27

score 1 · Accepted Answer · answered May 09 '14 at 05:39

Check http://ideone.com/wjRwi4 (and copied below)

But you might need to review how you're doing things:

Decide whether to use function pointers (or static member pointers) or method pointers (then you need an object to run the method on).
You probably need to think about how you want to apply this to a hierarchy.
Alternatively you can try function objects (i.e. a class/struct with an operator() defined).
Remember that is always easier if you create a typedef for the function/method pointer.
Check http://www.parashift.com/c++-faq/pointers-to-members.html

The code:

#include <iostream>
using namespace std;

class Man;

class Dog{
public:

    Man *man;
    void (Man::*callbackFunc)(void);

    void setCallback(Man *_man,void (Man::*_callbackFunc)(void)){
        callbackFunc=_callbackFunc;
        man=_man;
    }

    void bite();

};

class Man
{
public:
    void haveDogBiteYou(){
        Dog *myDog = new Dog();
        myDog->setCallback(this,&Man::sayAh); // How???
        myDog->bite();
    }

    void sayAh(){
        cout << "AHHHHHH!";
    }
};


void Dog::bite(){
    (man->*callbackFunc)();
}



int main() {
    Man m;
    m.haveDogBiteYou();
    return 0;
}

score 0 · Answer 2 · answered May 09 '14 at 05:25

You can change:

void sayAh(){
    cout << "AHHHHHH!";
}

to a static member function for your needs.

static void sayAh(){
    cout << "AHHHHHH!";
}

If you do that, you can simplify

    myDog->setCallback(this->sayAh);

to

    myDog->setCallback(sayAh);

Function pointers to pass on a method member

2 Answers2