c++ - 派生类私有(private)方法被调用

Question

我有一个指向派生类对象的基类指针。 foo() 方法在基类中是公共(public)的，但在派生类中是私有(private)的。基类 foo() 是虚拟的。因此，当我从基类指针调用 foo() 时，Vptr 表具有派生类 foo() 的地址，但它在派生类中是私有(private)的……所以它是如何被调用的。？？

我理解运行时多态性，我也理解访问说明符在编译时起作用，虚拟概念在运行时起作用。所以应该没有编译器错误。

我的问题是:这是一个循环漏洞，我们可以通过它调用派生类的私有(private)方法吗？或它的预期行为方式。对此行为的任何好的解释。

非常感谢。

代码:

class A
{
public:
    virtual void foo()
    {
        std::cout << "In A";
    }
};


class B:public A
{
private:
    void foo()
    {
       std::cout << "In B ??? Its Private Method :-( ";
    }
};

int main()
{
    A* ptr = new B();
    ptr->foo();
    return 0;
}

Answer 1

它是私有(private)方法，但由于它是虚拟的 - 它可以被调用。

n3690 11.5/1

The access rules (Clause 11) for a virtual function are determined by its declaration and are not affected bythe rules for a function that later overrides it.

这是为什么？由于

n3690 11.5/2

Access is checked at the call point using the type of the expression used to denote the object for which themember function is called (B* in the example above). The access of the member function in the class inwhich it was defined (D in the example above) is in general not known.