有一个用于使受保护的析构函数虚拟？ [英] Is there a use for making a protected destructor virtual?

问题描述

/*Child is inherited from Parent*/
class Parent {  
  public:  
    Parent () //Constructor
    {
        cout << "\n Parent constructor called\n" << endl;
    }
  protected:
    ~Parent() //Dtor
    {
        cout << "\n Parent destructor called\n" << endl;
    }
};

class Child : public Parent 
{
  public:
    Child () //Ctor
    {
        cout << "\nChild constructor called\n" << endl;
    }
    ~Child() //dtor
    {
        cout << "\nChild destructor called\n" << endl;
    }
};

int main ()
{
    Parent * p2 = new Child;          
    delete p2;
    return 0;
}

如果我使 Parent

推荐答案

只是为了解决这个问题，给一个例子：假设你有一个基类实现引用计数。你有一个 addRef 和一个 release 方法，你希望你的对象被销毁，如果（和 if）内部计数器通过调用 release 达到零。

Just to give one example: Say you have an base class which implements reference counting. You have an addRef and a release method and you want your object to be destroyed, if (and only if) the internal counter reaches zero through a call to release.

所以，首先你想要你的析构函数保护（因为你只想从 relase 中销毁对象）。

So, first you want your destructor protected (since you only want to destroy the object from within relase).

如果你计划从你的类派生，你也想要你的析构函数是虚拟的，因为你需要一个虚拟析构函数，每当你想通过指针来销毁一个子对象到基类（感谢@sharptooth的提示...）

If you plan to derive from your class, you also want to have your destructor virtual, since you need a virtual destructor whenever you want to destroy a child object through a pointer to a base class (thanks @sharptooth for the hint ...)

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