C ++：使用抽象方法创建抽象类，并覆盖子类中的方法 [英] C++: Create abstract class with abstract method and override the method in a subclass

问题描述

如何在C ++中创建一个抽象类与一些抽象方法，我想在子类中重写？文件应如何显示？ .h 有没有 .cpp ，如果是这样，它应该怎么样？

How to create in C++ an abstract class with some abstract methods that I want to override in a subclass? How should the .h file look? Is there a .cpp, if so how should it look?

在Java中它看起来像这样： / p>

In Java it would look like this:

abstract class GameObject
{
    public abstract void update();
    public abstract void paint(Graphics g);
}

class Player extends GameObject
{
    @Override
    public void update()
    {
         // ...
    }

    @Override
    public void paint(Graphics g)
    {
         // ...
    }

}

// In my game loop:
List<GameObject> objects = new ArrayList<GameObject>();
for (int i = 0; i < objects.size(); i++)
{
    objects.get(i).update();
}
for (int i = 0; i < objects.size(); i++)
{
    objects.get(i).paint(g);
}

将这段代码翻译成C ++对我来说已经足够了。

Translating this code to C++ is enough for me.

编辑：

我创建了代码，但是当我尝试遍历对象时， ：

I created the code but when I try to iterate over the objects I get following error:

Game.cpp:17: error: cannot allocate an object of abstract type ‘GameObject’
GameObject.h:13: note:   because the following virtual functions are pure within ‘GameObject’:
GameObject.h:18: note:         virtual void GameObject::Update()
GameObject.h:19: note:         virtual void GameObject::Render(SDL_Surface*)
Game.cpp:17: error: cannot allocate an object of abstract type ‘GameObject’
GameObject.h:13: note:   since type ‘GameObject’ has pure virtual functions
Game.cpp:17: error: cannot declare variable ‘go’ to be of abstract type ‘GameObject’
GameObject.h:13: note:   since type ‘GameObject’ has pure virtual functions

使用此代码：

vector<GameObject> gameObjects;

for (int i = 0; i < gameObjects.size(); i++) {
    GameObject go = (GameObject) gameObjects.at(i);
    go.Update();
}

推荐答案

virtual 默认情况下，除非您声明他们 final 。在C ++中，它是另一种方法：你需要显式声明你的方法 virtual 。要使它们成为纯虚拟，你需要将它们初始化为0 :-)如果你的类中有一个纯虚方法，它会自动变成抽象的 - 没有明确的关键字。

In Java, all methods are virtual by default, unless you declare them final. In C++ it's the other way around: you need to explicitly declare your methods virtual. And to make them pure virtual, you need to "initialize" them to 0 :-) If you have a pure virtual method in your class, it automatically becomes abstract - there is no explicit keyword for it.

在C ++中，你应该（几乎）总是为你的基类定义析构函数 virtual ，以避免棘手的资源泄露。所以我添加到下面的例子：

In C++ you should (almost) always define the destructor for your base classes virtual, to avoid tricky resource leaks. So I added that to the example below:

// GameObject.h

class GameObject
{
public:
    virtual void update() = 0;
    virtual void paint(Graphics g) = 0;
    virtual ~GameObject() {}
}

// Player.h
#include "GameObject.h"

class Player: public GameObject
{
public:
    void update();

    void paint(Graphics g);
}

// Player.cpp
#include "Player.h"

void Player::update()
{
     // ...
}

void Player::paint(Graphics g)
{
     // ...
}

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