Question

In the following, how can I make it such that the program uses the draw method from MainMenuScreen instead of the one from GameScreen?

class GameScreen {
public:
    virtual void GameScreen::draw() {
        cout << "Drawing the wrong one..." << endl;
    }
};

class MainMenuScreen : public GameScreen {
public:
    void MainMenuScreen::draw() {
        cout << "Drawing the right one..." << endl;
    }
};

class ScreenManager {
public:
    list<GameScreen> screens;

    // assume a MainMenuScreen gets added to the list

    void ScreenManager::draw()
    {
        for ( list<GameScreen>::iterator screen = screens.begin(); 
              screen != screens.end(); screen++ )
        {
            screen->draw(); /* here it uses the draw method from GameScreen, 
                               but I want it to use the draw method from              
                               MainMenuScreen */
        }
    }
};

PS: I do not want to make GameScreen::draw purely virtual, so please suggest something else.

Answer 1

how can I make it such that the program uses the draw method from
MainMenuScreen instead of the one from GameScreen?

You can’t, unless you call it on a pointer or reference whose actual type is MainMenuScreen.

 list<GameScreen> screens;

declares a list of objects, not pointers or references. If you add MainMenuScreen objects to it, they will lose type information because of object slicing and polymorphism will not work. You need:

 list<GameScreen*> screens;

or, better yet:

 list<shared_ptr<GameScreen> > screens;