C++虛擬類，子類和selfreference

Question

考慮這個類：

class baseController { 

    /* Action handler array*/ 

std::unordered_map<unsigned int, baseController*> actionControllers; 

protected: 

    /** 
    * Initialization. Can be optionally implemented. 
    */ 
    virtual void init() { 

    } 

    /** 
    * This must be implemented by subclasses in order to implement their action 
    * management 
    */ 
    virtual void handleAction(ACTION action, baseController *source) = 0; 

    /** 
    * Adds an action controller for an action. The actions specified in the 
    * action array won't be passed to handleAction. If a controller is already 
    * present for a certain action, it will be replaced. 
    */ 
    void attachActionController(unsigned int *actionArr, int len, 
      baseController *controller); 

    /** 
    * 
    * checks if any controller is attached to an action 
    * 
    */ 
    bool checkIfActionIsHandled(unsigned int action); 

    /** 
    * 
    * removes actions from the action-controller filter. 
    * returns false if the action was not in the filter. 
    * Controllers are not destoyed. 
    */ 
    bool removeActionFromHandler(unsigned int action); 

public: 

    baseController(); 

    void doAction(ACTION action, baseController *source); 

}; 

} 

和該亞類

class testController : public baseController{ 

    testController tc; 

protected: 

    void init(){ 
     cout << "init of test"; 
    } 



    void handleAction(ACTION action, baseController *source){ 

     cout << "nothing\n"; 

    } 

}; 

編譯器出現與該構件上的子類的錯誤

testController tc; 

..saying

error: field ‘tc’ has incomplete type 

但是，如果我刪除，我instatiate類它的工作......有沒有辦法避免這個錯誤？它看起來對我來說太奇怪了......

Answer 1

你的代碼試圖在其內部嵌入整個testController實例，這是不可能的。相反，你需要一個參考：

testController &tc; 

或指針

testController *tc; 

Answer 2

它不會編譯，因爲你聲明瞭一個成員變量'tc'，它是它自己的一個實例。你在子類中沒有使用tc;你這裏有什麼意圖？

Answer 3

您不能在該類本身內創建類的對象。可能你打算做的是保留一個指向類的指針。在這種情況下，你應該使用它作爲testController*順便說一句，你爲什麼要這樣做？我看起來有點奇怪。

Answer 4

one day someone asked me why a class can't contain an instance of itself and i said; 
    one day someone asked me why a class can't contain an instance of itself and i said; 
    one day someone asked me why a class can't contain an instance of itself and i said; 
     ... 

使用間接。一個（智能）指針或引用testController而不是testController。

Answer 5

（有點遲到了，但是......）

也許gotch4想鍵入這樣的事情？

class testController : public baseController 
{ 
public: 
    testController tc(); // <-() makes this a c'tor, not a member variable 

    // (... snip ...) 
};