C++雙指針成員訪問

Question

C++（Arduino的包裝器）的問題：我正在寫，其具有連接一個LCD一個拍攝時間了遊戲一個Arduino -

我有一個基類（Sprite），並從該另一類派生 - Alien,Missile和Player。 Alien類的構造函數也有私有成員pMissile（指向Missile類的指針） - '對象內的對象'將是一種描述我認爲的方式。 [當Alien觸發一個導彈，它通過其自身的（X，Y）座標轉換爲導彈和導彈有它自己的移動從Alien開始的方法的座標]

我的問題是：我如何通過Alien對象訪問導彈的座標？ 流線型代碼是下面，我也繪製的類的表示：

// Bass class - has a form/shape, x and y position 
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 getX() const { return x; } 
    unsigned int getY() const { return y; } 
    protected: 
    unsigned char *spacePtr; 
    unsigned int x, y; 
}; 


// Derived class "Missile", also a sprite and has a specific form/shape, and specific (x,y) derived from input sprite 
class Missile : public Sprite 
{ 
public: 
    Missile(): Sprite(&spaceMissile[0], 0, 0) {} 
    virtual void Move(); // its own method of moving 
}; 

// Derived class "Alien" - has a specific form/shape, and specific (x,y) position 
class Alien : public Sprite 
{ 
public: 
    Alien(); 
    virtual void Move(); // its own method of moving 
private: 
    Missile *pMissile; 
}; 

Alien::Alien(): Sprite(&spaceAlien[0], random(5, 75), random(4, 10)) 
{ 
    Missile MissileArray[MaxAmmoSize]; 
    pMissile = &MissileArray[0]; 
} 


void Alien::Move() 
{ 
    if(random(10) % 2 == 0) 
    x += 1; 
    if(random(10) % 3 == 0) 
    y += 1; 

    if((pMissile != NULL) && (random(10) == 1)) 
    { 
    pMissile->setCoord(x, y); 
    pMissile->Move(); // move the missile 
    pMissile++;  // move onto the next missile in the array 
    } 
    Render(); 
} 

/*****************************************************************************************/ 
Alien MONSTER; 
Player HERO; 
Alien *pMONSTER = &MONSTER; 

void loop() 
{ 
    display.clearDisplay(); 
    MONSTER.Move(); 
    HERO.Move(); 
    pMONSTER->getX(); // this is x location of MONSTER 
    **// how does pMONSTER access pMissile(x,y) within MONSTER.** 
    delay(100); 
    display.display(); 
} 

Embedded C++ Class interaction

Answer 1

的常用方法是吸氣函數添加到外來：

class Alien { 
public: 
    Missile* getMissile() { return pMissile; } 
} 

使用它：

Alien* a = getAlienFromSomewhere(); 
auto pMissile = a.GetMissile(); 
if (pMissile != NULL) { 
    x = pMissile->getX(); 
    y = pMissile->getY(); 
} 

Answer 2

我想你想通過外星人訪問你的導彈位置來測試你的英雄實體的碰撞，但是如果你需要保持你的導彈的軌道，你不應該用指向下一個導彈的指針「行走」如Alien::Move()所示。這樣做，您將失去數組開頭的參考。

恕我直言，我會做你的階級異己是這樣的：

// Bass class - has a form/shape, x and y position 
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& getX() const { return x; } 
    unsigned int& getY() const { return y; } 
    protected: 
    unsigned char *spacePtr; 
    unsigned int x, y; 
}; 


// Derived class "Missile", also a sprite and has a specific form/shape, and specific (x,y) derived from input sprite 
class Missile : public Sprite 
{ 
public: 
    Missile(): Sprite(&spaceMissile[0], 0, 0) {} 
    virtual void Move(); // its own method of moving 
}; 

// Derived class "Alien" - has a specific form/shape, and specific (x,y) position 
class Alien : public Sprite 
{ 
public: 
    Alien(); 
    ~Alien(); // a destructor to cleanup your missiles - arduino have almost no memory to handle leaks ;-) 
    virtual void Move(); // its own method of moving 

    inline Missile& getMissile(unsigned char n) { return pMissile[n];   } 
    inline Missile& operator[](unsigned char n) { return getMissile(n);  } 
    inline unsigned int& getX(unsigned char n) { return getMissile(n).getX(); } 
    inline unsigned int& getY(unsigned char n) { return getMissile(n).getY(); } 

private: 
    Missile *pMissile; 
    // adding the code to handle the count 
    unsigned char missileCount; 
}; 

Alien::Alien(): 
    Sprite(&spaceAlien[0], random(5, 75), random(4, 10)), 
    missileCount(0) 
{ 
    // this way of allocation creates a local object that is destroyed by the end of this scope 
    //Missile MissileArray[MaxAmmoSize]; 
    //pMissile = &MissileArray[0]; 

    // so you should do somethin like this 
    pMissile = new Missile[MaxAmmoSize]; 
} 

Alien()::~Alien() 
{ 
    delete[] pMissile; 
} 

void Alien::Move() 
{ 
    if(random(10) % 2 == 0) 
    x += 1; 
    if(random(10) % 3 == 0) 
    y += 1; 

    if((pMissile != NULL) && (random(10) == 1)) 
    { 
    // my proposal to fire it up 
    Missile& missile = pMissile[missileCount]; 
    missile->setCoord(x, y); 
    missile->Move(); // move the missile 
    missileCount++; // move onto the next missile in the array 
    } 
    Render(); 
} 

使用這樣的代碼，你可以通過訪問您的導彈的位置：

MONSTER.getX(0) += 1; 
MONSTER[0].getY() +=1; 
MONSTER.getMissile(1).getX() = 10; 

有一些清晰度我還建議將getX()和getY()方法重構爲x()和y()，因爲它們正在返回對類內容的引用（並且這樣做，您還應該將您的x和y成員到別的東西，或者你可以瘋狂與名稱衝突）。