复制构造函数无法识别继承的成员

Posted 2023-02-23

【中文标题】复制构造函数无法识别继承的成员

【英文标题】：Copy constructor doesn't recognize inherited members

【发布时间】：2017-06-03 02:07:01

【问题描述】：

我有两个班级：

class entity 
public:
  SDL_Rect pos;
  float x;
  float y;

  std::string spriteFile;
  SDL_Surface * spriteHandle;
  int rePos (int newX, int newY);
  int move (float deltaX, float deltaY, bool check); // Move x & y the specified amounts, also moving pos.x and pos.y for every integer increase of x or y
  int display (SDL_Surface * screenSurface); //Use SDL_BlipSurface to blip the image to the screen
  int loadImage (SDL_PixelFormat * format); //Load the image using the spriteFile string and optimize it using the SDL_PixelFormat of the Screen

  entity (std::string file, int w, int h);
  entity () ;
  ~entity ()  SDL_FreeSurface(spriteHandle);

  entity (const entity &old) : pos(old.pos), x(old.x), y(old.y), spriteFile(old.spriteFile) 
  spriteHandle = new SDL_Surface(*spriteHandle);
  

;

class multiEntity: public entity 
  /*
    Use multiEntity rather than entity when multiple images need to be blipped to different
    positions.
   */
private:
  static std::vector<stringBoolPair> deconstructed;
public:
  std::string entType;
  multiEntity (std::string file, int w, int h, std::string enttype) 
    entity(file, w, h);
    entType = enttype;
    bool found = false;
    for (int i = 0; i < deconstructed.size(); i++) 
      found = (enttype == deconstructed[i].str);
    
    if (found) deconstructed.emplace_back(enttype, false);
  

  multiEntity (const multiEntity& old) :
    spriteFile(old.spriteFile),
    x(old.x),
    y(old.y),
    spriteHandle(old.spriteHandle),
    pos(old.pos),
    entType(old.entType) 
    ~multiEntity () 
    for (int i = 0; i < deconstructed.size(); i++) 
      if (deconstructed[i].str == entType) 
    SDL_FreeSurface(spriteHandle);
    deconstructed[i].Bool = true;
      
    
  

  multiEntity& operator= (const multiEntity& old) 
    spriteFile = old.spriteFile;
    pos = old.pos;
    x = old.x;
    y = old.y;
    entType = old.entType;
    spriteHandle = old.spriteHandle;
    return *this;
  
;

当我尝试编译包含此代码的代码时，我收到一条错误消息，指出 class multiEntity does not have any field named 'pos'。除了entType 之外，复制构造函数中的所有变量都会发生这种情况。 我正在尝试做的是使用相同的 SDL_Surface 拥有entitys 的向量。因此，我觉得我应该创建一个单独的类，其中每个具有相同entType 的对象都具有相同的spriteHandle 值。这应该指向同一个图像，当我有 75 个图像实例我试图在屏幕上闪烁时，这是最有用的。我想使用vector的构造函数布局，以便复制信息而不是每次都创建一个新指针。

【问题讨论】：

Initialize parent's protected members with initialization list (C++)的可能重复

您无需发布所有这些代码即可指出您遇到的问题。 An example

谢谢@PaulMcKenzie。我会尽量记住这一点，并在未来更具描述性。

【参考方案1】：

您不能在派生类的复制构造函数中初始化基类的成员；它们应该通过基类的复制构造函数进行初始化。您应该只在成员初始化器列表中调用它：

multiEntity (const multiEntity& old) :
    entity(old),         // initialize entity's members via entity::entity(const entity&)
    entType(old.entType) // initialize multiEntity's member entType 

如果基类的复制构造函数的行为不是你想要的，你可以在派生类的构造函数体中做一些赋值，例如

multiEntity (const multiEntity& old) :
                         // nothing specified, same as write entity() here
                         // entity's members will be initialized via entity::entity()
    entType(old.entType) // initialize multiEntity's member entType 

    // perform assignment here
    spriteFile = old.spriteFile;
    x = old.x;
    y = old.y;
    spriteHandle = old.spriteHandle;
    pos = old.pos;

【讨论】：

那么我如何确保 SDL_Surface 是浅拷贝？我希望它复制父类中的数据，但只复制子类中的地址。

@BobPaw 答案已修改。