我正在尝试引入一个简单的状态模式，之前在这里参考了一些优秀的教程：http://gameprogrammingpatterns.com/state.html
我已经完成了其中一半的教程，并且正试图通过将每个状态放进基类来复制静态实例。然而，在切换状态时，g++会抛出以下错误。
state_test.cpp: In member function ‘virtual void Introduction::handleinput(Game&, int)’:
state_test.cpp:55:16: error: cannot convert ‘Playing*’ to ‘GameState*’ in assignment
game.state_ = &GameState::play;
^
现在，我知道错误涉及指针的转换，但我真的很难看出如何修复它。当我跟随这个人的代码时，我有点期望它会起作用，但因为他在不断更改并试图加强最佳实践，所以我没有他完整的源代码可供跟随。然而，在我继续进行本教程的其余部分之前，我觉得理解代码是很重要的。
以下是我创建的代码，试图复制他的状态系统：
#include <iostream>
class Game;
class Introduction;
class Playing;
class GameState
{
public:
static Introduction intro;
static Playing play;
virtual ~GameState() {std::cout << "an undefined GameState has been destroyed" << std::endl;}
virtual void handleinput(Game& game, int arbitary) {}
virtual void update(Game& game) {}
};
class Game
{
public:
Game()
{}
~Game()
{}
virtual void handleinput(int arbitary)
{
state_->handleinput(*this, arbitary);
}
virtual void update()
{
state_->update(*this);
}
//private:
GameState* state_;
};
class Introduction : public GameState
{
public:
Introduction()
{
std::cout << "constructed Introduction state" << std::endl;
}
virtual void handleinput(Game& game, int arbitary)
{
if (arbitary == 1)
game.state_ = &GameState::play;
}
virtual void update(Game& game) {}
};
class Playing : public GameState
{
public:
Playing() {std::cout << "constructed Playing state" << std::endl;}
virtual void handleinput(Game& game, int arbitary)
{
if (arbitary == 0)
game.state_ = &GameState::intro;
}
virtual void update(Game& game) {}
};
int main(int argc, char const *argv[])
{
Game thisgame;
return 0;
}
有什么想法，为什么我的实现无法编译？
编辑：
作为之前的辅导的回应，我非常感激，我修改了代码。我首先将它们放在不同的文件中，但是对于这样少量的测试代码来说，这更麻烦。我只是重写了一个声明类的头文件，然后在.cpp文件中定义了它们。
这是.h文件：
class Introduction;
class Playing;
class Game;
class GameState;
class GameState
{
public:
static Introduction intro;
static Playing play;
virtual ~GameState();
virtual void handleinput(Game& game, int arbitary);
virtual void update(Game& game);
};
class Introduction : public GameState
{
public:
Introduction();
virtual void handleinput(Game& game, int arbitary);
virtual void update(Game& game);
};
class Playing : public GameState
{
public:
Playing();
virtual void handleinput(Game& game, int arbitary);
virtual void update(Game& game);
};
class Game
{
public:
Game();
~Game();
virtual void handleinput(int arbitary);
virtual void update();
GameState* state_;
};
以下是 .cpp 文件：
#include <iostream>
#include "state.h"
GameState::~GameState()
{std::cout << "Exiting Game State Instance" << std::endl;}
void GameState::handleinput(Game& game, int arbitary)
{}
void GameState::update(Game& game)
{}
Game::Game()
{}
Game::~Game()
{}
void Game::handleinput(int arbitary)
{
state_->handleinput(*this, arbitary);
}
void Game::update()
{
state_->update(*this);
}
Introduction::Introduction()
{
std::cout << "constructed Introduction state" << std::endl;
}
void Introduction::handleinput(Game& game, int arbitary)
{
if (arbitary == 1)
game.state_ = &GameState::play;
}
void Introduction::update(Game& game) {}
Playing::Playing()
{
std::cout << "constructed Playing state" << std::endl;
}
void Playing::handleinput(Game& game, int arbitary)
{
if (arbitary == 0)
game.state_ = &GameState::intro;
}
void Playing::update(Game& game) {}
int main(int argc, char const *argv[])
{
Game mygame;
return 0;
}
我仍然无法让它工作。之前的错误已经消失了，但我仍然很难访问“introduction”的静态实例并在基础类中播放。抛出的错误是：
/tmp/ccH87ioX.o: In function `Introduction::handleinput(Game&, int)':
state_test.cpp:(.text+0x1a9): undefined reference to `GameState::play'
/tmp/ccH87ioX.o: In function `Playing::handleinput(Game&, int)':
state_test.cpp:(.text+0x23f): undefined reference to `GameState::intro'
collect2: error: ld returned 1 exit status
我本以为我已经搞清楚了！太沮丧了！
我应该补充一下，RustyX提供的答案确实可以编译，但是我必须将“playing”和“introduction”的实例移出类定义，这样我就不能将它们设置为静态的了。我认为这很重要，因为我只需要一个实例，并且希望尽早初始化它们。