HOW TO: Class functions pointers (C++) - c++

Question

I have some problems with understanding function pointers. Although I've read lots of topics on this I still have problems with the follow case.
My example is simple - I have a joystick class which has some function pointers as well as functions through which these pointers can be assigned and I don't know how to do this properly.
I'll try to keep it simple:
class Joystick {
void (Player::*OnShootKeyPressed)(); // pointer that takes no arguments and returns nothing
void SetCallback(void (Player::*f)) {
OnShotKeyPressed = f;
}
}
class Player {
void OnShootAction() { ...do the shooting...}
void Initialize() {
Joystick* joy = pInputMng->GetJoystick();
joy->SetCallback( &Player::OnShootAction() );
}
}
--Edited after Captain Obvlious comment--
That's one short example of what I want to achieve and I don't seem to understand these function pointers correctly. What am I doing wrong?
I appreciate all the help in advance!

Answer 1

I love function pointers. I consider them among my best personal friends. But this is probably not the time for them. When you have whole objects calling each other back and forth, Just pass the object.
If you need greater decoupling between the objects, build an interface. I'll go with the interface route because why not? Once you've seen the hard way, the easy way's easy.
First, define an interface for users of the joystick
class ButtonUser
{
virtual void OnShootAction() = 0; // function to be implemented by children
virtual void OnJumpAction() = 0;
virtual void OnDeathBlossomAction() = 0;
...
}
Now a joystick that uses the button interface and knows absolutely nothing about Player
class Joystick {
ButtonUser * pUser;
void SetCallback(ButtonUser * puser) {
pUser = puser;
}
void OnKeyPressed(key) {
if (pUser != NULL) {
switch( key ) {
case SHOOT:
pUser->OnShootAction();
break;
case JUMP:
pUser->OnjumpAction();
break;
case DB:
pUser->OnDeathBlossomAction();
break;
...
}
}
}
}
And Player installs itself as Joystick's user
class Player: public ButtonUser{
void OnShootAction() { ...do the shooting...}
void OnJumpAction() {...jump...};
void OnDeathBlossomAction() {...blow $#!+ up!...}
...
void Initialize() {
Joystick* joy = pInputMng->GetJoystick();
joy->SetCallback( this );
}

Answer 2

CORRECTED CODE & ANSWER
1.) I was having some problems with namespaces not mentioned in the question so I wasn't able to create a function.
Both classes were under the namespace so the function for assigning a function pointer was rejected:
void SetCallback(void (ehJoystick::*f)())
It was required to be this instead:
void SetCallback(void (eg::ehJoystick::*f)())
But then, compiler didn't accept the namespace infront of that. I thought I was doing something wrong elsewhere but there problem was there all the time.
2.) I didn't know you need an object reference where you want to call a member function pointer. Following code is correct and working.
class Joystick {
Player* pPlayer;
void (Player::*OnShootKeyPressed)() = NULL; // pointer that takes no arguments and returns nothing
void SetCallback(void (Player::*f)(), Player *p) {
OnShotKeyPressed = f;
pPlayer = p; // we need a reference to the object
}
void OnKeyPressed(key) {
if( key == SHOOT && OnShootKeyPressed != NULL ) {
(pPlayer->*OnShootKeyPressed)(); //that's how the function is called
}
}
class Player {
void OnShootAction() { ...do the shooting...}
void Initialize() {
Joystick* joy = pInputMng->GetJoystick();
joy->SetCallback( &Player::OnShootAction, this );
}