在C ++中定义枚举类型的静态变量

Question

class Game
{
public:
    static void Start();

private:
    static bool IsExiting();
    static void GameLoop();

    static void ShowSplashScreen();
    static void ShowMenu();

    enum GameState { Uninitialized, ShowingSplash, Paused,
                    ShowingMenu, Playing, Exiting };

    Game::GameState Game::_gameState = Game::Uninitialized;
    static sf::RenderWindow _mainWindow;
};
Game::GameState Game::_gameState;
RenderWindow Game::_mainWindow;

现在出现错误，该错误会首先运行

void processEvents(){// error: first defined here ???
    Event event;
    while(App.pollEvent(event)){
        if(event.type == Event::Closed)
                App.close();
    }
}

还有其他错误，例如函数中的“ Game :: _ gameState”的多个定义，它在Game类中声明的其他函数中也给出相同的错误

void Game::Start(void) { // multiple definition of `Game::_gameState'
    if (_gameState != Uninitialized)
        return;

    _mainWindow.create(VideoMode(1200, 900, 32), "Game",
            Style::Close);
    _gameState = Game::ShowingSplash;

    while (!IsExiting()) {
        GameLoop();
    }

    _mainWindow.close();
}

我更正了错误，但又出现了一个

while (!IsExiting()) {  //undefined reference to Game::IsExiting
    GameLoop();
}

_mainWindow.close();

}

我不知道这是静态布尔函数，其他函数也能正常工作，但是这是布尔函数，给我错误

Answer 1

GameState枚举在Game类的范围内声明。 因此，当您在该类的范围之外引用它时，必须使用完全限定的类型名称（包括定义_gameState字段的实例。我还建议您为其提供一些初始值。例如：

Game::GameState Game::_gameState = Game::Uninitialized;

希望能帮助到你！

Answer 2

由于enum GameState包含在class Game您需要相应地调整变量的范围：

Game::GameState Game::_gameState;