architecture - C++ GameState management

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 would like to know how other people implement their game state management, i.e. what you like the most and why you like it. Also, any tutorials/code examples that are generally about game state would also be much appreciated.

Answer

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++)