復制構造函數無法識別繼承的成員

Question

我有兩節課：

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;
  }
};

當我嘗試編譯包含此代碼的代碼時，收到一條錯誤消息，指出class multiEntity does not have any field named 'pos' 。 復制構造函數中除entType之外的所有變量都會發生這種情況。 我試圖做的是使用相同的SDL_Surface擁有一個vector entity 。 因此，我覺得我應該創建一個單獨的類，其中每個具有相同entType對象的spriteHandle都具有相同的值。 這應該指向同一張圖片，當我有75個實例的圖片實例想在屏幕上顯示時，這是最有用的。 我想使用vector的構造函數布局，以便將信息復制過來，而不是每次都創建一個新的指針。

Answer 1

您不能在派生類的副本構造函數中初始化基類的成員。 它們應該通過基類的副本構造函數進行初始化。 您應該只在成員初始化列表中調用它：

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

如果基類的復制構造函數的行為不是您想要的，則可以在派生類的構造函數主體中進行一些分配，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;
}