class function pointer

hello
Is there a known way to assign a class method to a function pointer?

I tried this, which doesn't work:

Code:

---

class MyClass {
        void func ()
        {
                ...
        }
}

int main ()
{
        void (*fptr) ();        //function pointer
        MyClass foo;                //instance

        fptr = foo.func;
}

---

compiler (g++) says:
error: argument of type ‘void (Class:: )()’ does not match ‘void (*)()’

Class functions has a special syntax:
void (MyClass::*)()

But why would you actually want to do that? The whole point of having classes is that they have member functions. With virtual member functions, you can create the same effect, but avoid the actual function pointer mess - yes, internally the compiler generates roughly the same code, but it's much easier to read and use.

--
Mats

ok thanks
but, what if I wish to use the pointer with different classes?

Quote:

---

Originally Posted by matsp

But why would you actually want to do that?

---

The main use the fpointer to call the function I need
eg:
STATE = game -> call Game::main ()
STATE = menu -> call Menu::main ()

You're thinking in a C way. You probably want something like this in C++.

Code:

---

class base {
public:
    virtual void main() = 0;  // no really, Elysia, this void main is okay :)
};

class game : public base {
public:
    virtual void main() {  // "virtual" not technically required
        // ...
    }
};

class menu : public base {
public:
    virtual void main() {  // "virtual" not technically required
        // ...
    }
};

// and so on

base *p = new menu;
p->main();

---

Code:

---


fptr = MyClass::foo.func;

---

should work, but i woudlnt recommend it. Why exactly do you need a function pointer to a member function?

Is thewre some reason you cant make it a friend function to all the clsses its associated with?

Well, I'm not used with class stuff like virtual functions, inheritance and friendship...
so I'm trying to learn more about at the moment, since I'm a bit confused now :)

However I've encountered another problem using a function-pointer stack:

Code:

---

#include <iostream>
using namespace std;

#include <stack>

void menu ()
{
        cout << "hello\n";
}

typedef void (*fptr) ();

int main ()
{
        stack<fptr> State;

        fptr temp;
        temp = menu;

        State.push (temp);
        State.top ();

        return 0;
}

---

this code didn't print "hello": what's wrong?

Well, you're not calling the function, are you?
It should be something like
State.top()();
or maybe
( State.top() )();
Seeing as top is a function that returns a reference to the object at the top of the stack.

Aaargh you're right :)
I was missing that detail indeed
thanks