C 中的视觉理解抽象

从Java到C ，我正在尝试通过对象取向理解抽象。

为了将其放入一个实用的示例中，我正在使用SFML库来开发一个小型游戏。但是，这个问题与此无关，只需将其视为背景信息即可。无论如何，游戏的工作方式是通过多种不同状态进行处理。在这种情况下2：

1. 菜单状态：绘制游戏的菜单，游戏将在此处开始。

2. 游戏状态：此状态控制游戏，将更新实体并绘制它们。

为此，我创建了以下类：

gamestatemanager.h

#ifndef GAMESTATEMANAGER_H
#define GAMESTATEMANAGER_H
#include <SFML/Graphics.hpp>
#include <iostream>
#include "GameState.h"
class GameStateManager
{
public:
    // Constructor
    GameStateManager();
    // State variables
    static const int NUMGAMESTATES = 2;
    static const int MENUSTATE = 0;
    static const int GAMESTATE = 1;
    // Public Functions
    void set_state(int state);
    void update();
    void draw(sf::RenderWindow &win);
    void input(sf::Event event);
private:
    // Array of gamestates
    GameState game_states[];
    // The current state
    int current_state;
    // Private functions
    void load_state(int state);
    void unload_state(int state);
};
#endif

gamestate.h

#ifndef GAMESTATE_H
#define GAMESTATE_H
#include <iostream>
#include <SFML/Graphics.hpp>
#include "GameStateManager.h"
class GameState
{
protected:
    GameStateManager gsm;
public:
    virtual void init() = 0;
    virtual void update() = 0;
    virtual void draw(sf::RenderWindow &win) = 0;
    virtual void input(sf::Event event) = 0;
};
#endif

现在，您可能已经注意到游戏州经理中的游戏阵列吗？这提供了我不理解的错误：零尺寸的数组。这是否意味着需要在标题文件中进行初始化？此外，编译器提到了一个抽象类的数组？

第二个问题是抽象游戏类中的字段GSM无法识别并提出另一个错误：缺少类型的指定词。

现在要使事情变得更复杂，我有以下课程：菜单。该课程旨在扩展游戏。

Menustate.h

#ifndef MENUSTATE_H
#define MENUSTATE_H
#include "GameState.h"
class MenuState: public GameState
{
public:
    MenuState(GameStateManager gsm);
    void init();
    void update();
    void draw(sf::RenderWindow &win);
    void input(sf::Event event);
private:
    sf::Texture title_texture;
    sf::Sprite title_sprite;
};
#endif

如前所述，此类将控制游戏的菜单。

实现gamestateManager如下：

gamestatemanager.cpp

/*
 * GameState Manager will take care of the various states of the game.
 * In particular there will be two states: Menu or Ingame. GameStateManager
 * will load and unload each state as needed.
 *
 * Author: Ben Euden
 * Date: 2/5/2014
 */
#include "GameStateManager.h"
// Class Constructor
GameStateManager::GameStateManager()
{ 
    game_states = game_states[NUMGAMESTATES];
    current_state = MENUSTATE;
    load_state(current_state);
}
/*
 * Load the current game by creating and initialising the state
 * then storing it in the game_states array.
 * @Param state The state we wish to load.
 */
void GameStateManager::load_state(int state)
{
    if(state == MENUSTATE)
        game_states[state] = MenuState(this);
    //if(state == GAMESTATE)
        //game_states[state] = MainGameState(this);    // Not implemented yet.
}
/*
 * Unload the state we loaded with load_state
 */
void GameStateManager::unload_state(int state)
{
    game_states[state] = NULL;
}
void GameStateManager::set_state(int state)
{
    unload_state(state);
    current_state = state;
    load_state(state);
}
void GameStateManager::update()
{
    try{
        game_states[current_state].update();
    }
    catch(int e)
    {
        std::cout << "Exception occured during update of game state" << e << std::endl;
    }
}
void GameStateManager::draw(sf::RenderWindow &win)
{
    try{
        game_states[current_state].draw(&win);
    }
    catch(int e)
    {
        std::cout << "Exception occured when trying to draw gamestate: " << current_state << "Exception number: " << e << std::endl;
    }
}
void GameStateManager::input(sf::Event event)
{
    game_states[current_state].input(event);
}

and菜单如下：

/*
 * This class extends the Game State header and will deal with the menu of the game
 * this includes drawing the correct text to the screen, moving the selector and
 * either exiting, bringing up about or starting the game.
 *
 * Author: Ben Euden
 * Date: 2/5/2014
 */
#include "MenuState.h"

MenuState::MenuState(GameStateManager gsm)
{
    gsm = gsm;
    init();
}
void MenuState::init()
{
    title_texture = sf::Texture();
    title_texture.loadFromFile("sprites/Title.png");
    title_sprite = sf::Sprite();
    title_sprite.setTexture(title_texture);
    title_sprite.setPosition(512, 200);
}
void MenuState::update(){}
void MenuState::draw(sf::RenderWindow &win)
{
    win.draw(title_sprite);
}
void MenuState::input(sf::Event event)
{
}

请忽略成文学的方法和位置。在这一点上，我开始尝试在错误出现时尝试编译项目（我正在使用Visual Studio）。

现在了解到尚未实施Maingamestate，但即使使用壁andate，我敢肯定，我在这里还缺少一些重要的东西，因为我仍在学习C 。考虑到这一点也请原谅任何公约等的违反，我正在学习，所以请随意纠正我，最好现在学习正确的方法，而不是养成不良习惯。

总而言之，我想理解为什么我会收到以下错误：

protected:
    GameStateManager gsm;

这会产生错误：缺少';'GSM之前。

GameState game_states[];

产生以下错误的错误：零大小数组，不允许抽象类的数组。

我相信，如果我修复了其余的，那么

感谢您的耐心，时间和帮助。

euden