How to access variables of uninitialized class?

Question

So I've gone with a somewhat singleton approach to my game class:

#include "myGame.h"

int main () {
    myGame game;
    return game.Execute();
}

But now I need to define a class that accesses variables in the instance of myGame.

class MotionState {
    public:
    virtual void setWorldTransform (...) {
        VariableFromMyGameClass++;            //<-- !?
        ...}
};

I'm trying to integrate this class into my project from an example that just uses globals. How can I access variables of myGame class in the definition of new classes? Should I give up on my singleton approach?

Answer 1

If you want to continue using the singleton approach, you could benefit from a proper implementation of the singleton design pattern in C++.

Essentially, you define your class as follows:

class myGame {
private:
    static myGame* _instance;
    // Other private members.

public:
    static myGame* Instance();
    // Other public members.
};

And then the Instance function looks like this:

myGame* myGame::Instance() {
    if (!_instance)
        _instance = new myGame();

    return _instance;
}

This way, you can call myGame::Instance() to get your singleton class, and invoke whatever modifier or function you need, from anywhere in your code.

You might also be interested in: https://stackoverflow.com/questions/1008019/c-singleton-design-pattern

Answer 2

My thoughts-

A singleton implementation is a great way to just have one instance. But if your interested, another way, which I use ALL the time is a completely static class. By declaring all your functions and variables in your "MyGame" class as static you can just use the '::' operator (ex: MyGame::VariableFromMyGameClass++;) Also, as an added benefit, you can force no object creation of the class by declaring the default constructor 'private'.

Just thought I'd contribute :)

-MasterBaldwin