C++ c++；虚类、子类和自引用

以这一类为例：

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);

};

}

…说

error: field ‘tc’ has incomplete type

---

但是如果我把它移除，然后重新启动这个类，它就会工作。。。有没有办法避免这个错误？？？它看起来很奇怪……

它无法编译，因为您正在声明一个成员变量“tc”，它本身就是一个实例。您没有在子类中使用tc；您在这里的目的是什么？

您不能在该类本身内部创建该类的对象。可能您打算做的是保留一个指向该类的指针。在这种情况下，您应该将其用作

testController*

BTW，您为什么要这样做？我觉得有点奇怪。

您的代码试图将整个

testController

实例嵌入自身，这是不可能的。相反，您需要一个引用：

testController &tc;

还是指针

testController *tc;

使用间接方式。指向testController而不是testController的（智能）指针或引用。

（派对有点晚，但是…）

也许gotch4的意思是输入这样的东西

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

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

class testController:公共baseController
{
公众：
testController tc（）//您在另一个问题中提到了您熟悉Java，但对C++是新的。一个重要的区别是类变量声明的意义，例如“代码>类对象；。在C++中，这个变量是类<代码>的实际实例，而不是java中的引用。我只是在测试基类…它打算容纳许多相同类型的控制器谢谢…但是五年后我真的不记得为什么我会有这个问题！当然，但是其他人将来可能会偶然发现这个问题，提示“也许你想添加构造函数而不是成员变量声明？”可能会对他们有所帮助。
testController *tc;

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;
      ...

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

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