[Solved] How to use function pointers in different classes?

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If you absolutely need to call a function by pointer you will need to use a pointer to member function instead of a pointer to function. A pointer to member function has a different declaration syntax that includes the class type the function belongs to. In your case the parameter declaration would look like int (A::*cp)(). You will also need to change the declaration of the f member variable to int (A::*f)().

In order to call a pointer to member function you need to have a pointer to an object of the type the function belongs to. You also need to use one of the pointer to member operators; ->* or .*

void call(A* c, int (A::*f)())
{
    (c->*f)(); // call member function through pointer
}

The extra set of parenthesis is required due to the order of precedence of operators.

The following code includes the changes necessary for you to use pointer to member functions.

class A
{
public:

    class B
    {
    public:

        // Take a pointer to member function.
        B(int(A::*cf)())
        {
            f = cf;
        }

        void call(A* c)
        {
            (c->*f)();
        }

        int (A::*f)();  // pointer to member function
    };


    B *b;


    A()
    {
        b = new B(&A::a);
    }


    int a()
    {
        return 0;
    }
};

int main()
{
    A a;
    a.b->call(&a);
}

I also recommend that you consider using std::function and std::bind (or their Boost equivalents if you do not have a C++11 compiler).

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solved How to use function pointers in different classes?