C++ GameState management

Question

I have been attempting to make a game engine in C++ and have come across the dilemma of game state management. I have done a lot of research and found numerous ways of accomplishing from game engine with derived classes to using enums and I would like to know the most effective/efficient way of managing game states.

EDIT
i just wonted to quickly rephrase my question...i would like to now how u implement your game state management...what you like the most and why you like it..also any tutorials/code examples generally about game state that would also be much appreciated.

Answer 1

In most of my games (that are all small in scope) I have used an enum and a switch (in some cases an if..else if...) and it has always been sufficiently fast. I've never had more than a few states, which helps.

enum GameStates
{
    Running = 1,
    Menu = 2,
    Credits = 3
}

// update loop

switch(this.CurrentState)
{
    case GameStates.Running:
        UpdateRunning(gameTime);
        break;
    case GameStates.Menu:
        UpdateMenu(gameTime);
        break;
    case GameStates.Credits:
        UpdateCredits(gameTime);
        break;
    // add more states here
}

void UpdateRunning(GameTime gameTime)
{
    if(running == null) LoadRunning(); // 
    // perform the rest of your game logic
}

This gives you a few things worth mentioning:

1. You can change state anywhere, as long as you have a pointer to your main class.
2. You can load/unload as necessary to save memory (if your game is big it might be nice)
3. You've kept your very simple and easy to follow. This is the single most important thing a programmer can do IMO.

(Please excuse my C#/XNA style this was copy/pasted and tweaked, shouldn't be to hard to adapt to C++)

Answer 2

The most common approch to GameState algorithm is to have some game states and program can freely choose to run any one of them, this means there is a GameDirector which has a pointer to current running state, and in each update cycle it'll call 'currentState->run()`. in this approch GameDirector is a singleton and every one can access it, and also every one can change game state. also gameDirector is responsible for game's main loop.

class Director
{
private :
    RendererEngine* rEngine;
    SoundEngine* sEngine;
    PhysicsEngine* pEngine;
    GameState* gState;
    static Director* instance;
    Director()
    {
        rEngine = sEngine = pEngine = gState = NULL;
    }
public :
    static Director* GetDirector()
    {
        if (instance == NULL)
            instance = new Director;
    }

    RenderEngine* getRenderEngine() {return rEngine;};
    SoundEngine* getSoundEngine() {return sEngine;};
    PhysicsEngine* getPhysicsEngine() {return pEngine;};

    void runGame(GameState* pState)
    {
        return instace;
        rEngine = new RenderEngine;
        sEngine = new SoundEngine;
        pEngine = new PhysicsEngine;
        gState = pState;
        gState->onEnter();
        while (gState)
        {
            gState->onUpdate();
            gState->onDraw();
            rEngine->swapBuffers();
        }
    }

    void changeState(GameState* pState)
    {
        gState -> onEnd();
        gState = pState;
        if (gState)
            gState -> onEnter();
    }
}

Answer 3

Something I found interesting when looking around was the Advanced Ogre Framework which has a state management implementation. It is designed for the Ogre3D rendering engine but that part can be replaced pretty easily.

http://www.ogre3d.org/tikiwiki/Advanced%20Ogre%20Framework