嵌入式C ++类交互 [英] Embedded C++ Class interaction

问题描述

我正在继续一个嵌入式微控制器（Arduino）的游戏，我有一个关于类互动的问题 - 这个问题从我以前的问题继续这里，我基于我的代码建议sheddenizen（见回复给定的链接在这里）：

I'm continuing with a game for an embedded microcontroller (Arduino), and I have a question on class interaction -- this question continues from my previous question here and I have based my code on the suggestion of sheddenizen (see response to the given link in 'here'):

我有三个继承自一个基类的类 -

I have three classes that inherit from a base class-

（i） class Sprite - （bass class）在LCD上具有位图形状和（x，y）位置

(i) class Sprite - (bass class) has a bitmap shape and (x,y) position on an LCD

（ii）class Missile：public Sprite （x，y）并且还采用obj

(ii) class Missile : public Sprite - has a specific shape, (x,y) and also takes a obj

（iii） class Alien：public Sprite

（iv） class Player：public Sprite -

有不同的（虚拟）移动方法，并显示在LCD上：

They all have different (virtual) method of moving and are shown on the LCD:

我的简化代码在下面 - 具体来说，我只想要导弹在某些情况下发射：当导弹是创建它需要一个对象（x，y）值，如何在继承类中访问传递的对象值？

// Bass class - has a form/shape, x and y position 
// also has a method of moving, though its not defined what this is  
class Sprite
{
  public:
    Sprite(unsigned char * const spacePtrIn, unsigned int xInit, unsigned int yInit);
    virtual void Move() = 0;
    void Render() { display.drawBitmap(x,y, spacePtr, 5, 6, BLACK); }
    unsigned int X() const { return x; } 
    unsigned int Y() const { return y; }
  protected:
    unsigned char *spacePtr;
    unsigned int x, y;
};

// Sprite constructor
Sprite::Sprite(unsigned char * const spacePtrIn, unsigned int xInit, unsigned int yInit)
{
  x = xInit;
  y = yInit;
  spacePtr = spacePtrIn;
}

/*****************************************************************************************/
// Derived class "Missile", also a sprite and has a specific form/shape, and specific (x,y) derived from input sprite
// also has a simple way of moving
class Missile : public Sprite
{
public:
   Missile(Sprite const &launchPoint): Sprite(&spaceMissile[0], launchPoint.X(), launchPoint.Y()) {}
   virtual void Move();
};

void Missile::Move()
{
  // Here - how to access launchPoint.X() and launchPoint.Y() to check for 
  // "fire conditions" 
  y++;
  Render();
}


// create objects
Player HERO;
Alien MONSTER;
Missile FIRE(MONSTER);

// moving objects 
HERO.Move(); 
MONSTER.Move();
FIRE.Move();  

推荐答案

Missile 是 Sprite 的子类，您可以访问 Sprite :: x 和 Sprite :: y ，就好像他们是导弹的成员一样。这是通过简单地写 x （或如果你坚持认为 this-> x ）。

Since Missile is a subclass of Sprite you can access Sprite::x and Sprite::y as if they were members of Missile. That is by simply writing x (or this->x if you insist).

现在，构造函数中的 launchpoint 引用已经消失，因此您的 Missile :: Move <

The launchpoint reference that you got in the constructor is gone by now, so your Missile::Move memfunction cannot access it any more.

如果在此期间成员 x 和 y 更改，但您想要原始值，您可以保存对 launchpoint 这可能是危险的，它被毁灭），或者你必须保持原始坐标的副本。

If in the meantime the members x and y changed, but you want the original value, you can either save a reference to launchpoint (which might be dangerous, it is destroyed) or you have to keep a copy of the original coordinates.

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