Member Function Pointer Mayham

EDIT: Skip this and read my reply. It gives a much more clear scenerio.


I need to make use of a function pointer to a member function. I am running into many issue's with this.

The problem is I am trying to store a function pointer which is a member of class 'State' but I am passing in a function from class 'GameState' which derives from 'State'.

Here is the snippets to best describe my dilema:

PHP Code:

---

//An abstract State class which contains this virtual method
/**
* Handles messages for the gameWindow
*/
    virtual LRESULT CALLBACK messageHandlerWindow(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) = 0;


//Here is a class which derives from the State class and overrides the method
/**
* Handles messages for the gameWindow
*/
LRESULT CALLBACK GameState::messageHandlerWindow(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)


//Here is a GraphicLayer class which needs to be able to
//take in a function pointer to its messageHandlerWindow(..)
//This messageHandler has to be generic because there are more states
//than just the gameState seen above.  

//Member in GraphicLayer to store the func pointer
//non-static State specific message handler
    LRESULT (__stdcall State::*m_pMsgHandler)(HWND, UINT, WPARAM, LPARAM);

/**
* Attach a STATE specific message handler to the window
* The static message handler does nothing but pass its messages to this
* @param msgHandler - A function pointer to the msgHandler
*/
void GraphicLayer::attachWindowMessageHandler(LRESULT (__stdcall State::*msgHandler)(HWND, UINT, WPARAM, LPARAM))
{
    m_pMsgHandler = msgHandler;
} 


---

The errors I get just keep running me in circles.

error C2664: 'GraphicLayer::attachWindowMessageHandler' : cannot convert parameter 1 from 'LRESULT (__stdcall GameState::* )(HWND,UINT,WPARAM,LPARAM)' to 'LRESULT (__stdcall State::* )(HWND,UINT,WPARAM,LPARAM)'
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast


Also, how would I write the return for that... It seems rather complex:

PHP Code:

---

/**
* Returns the message handler which was attached to the graphicLayer
* @return msgHandler - The pointer attached to the graphic layer
*/
LRESULT (__stdcall State::*GraphicLayer::getAttachedWindowMessageHandler())(HWND, UINT, WPARAM, LPARAM)
{
    return m_pMsgHandler;
} 


---

Lemme make life simplier on everyone:

class A
{
virtual void foo() = 0;
}

class B : public A
{
void foo() {};
}

class C : public A
{
void foo() {};
}

I need to be able to store the member function pointer to foo() in one place, but it must be able to store the B:foo() or the C:foo() in one pointer. Since they both derive from A:foo() I figure this would be easy. However some reading has shown this to be either impossible or extremely complex.

The problem doesn't make sense. The point of virtual functions is that the correct one is called automatically. So you shouldn't store a pointer to the member function, you should store just a pointer to a State object and call the virtual on that.