今天写代码竟然发现，private成员函数竟然可以在类的外部调用，开始以为是C++设计的缺陷。但是逐步深入才知道C++多态的博大精深。

#include <iostream>using namespace std; class Base{public: virtual void Func() {  cout<<"base"<<endl; }};class Derived : public Base{private: void Func()  {  cout<<"derived"<< endl; }};int main(){ Base *d = new Derived; d->Func( ); delete d;  return 0;}

查看了一下资料，发下了下面的内容，这下一下子就明了了。

/*参考C++ Standard ISO/IEC 14882:2003(E) 第11.6节:11.6 Access to virtual functions [class.access.virt]The access rules (clause 11) for a virtual function are determined by its declaration and are not affected by the rules for a function that later overrides it. [Example:*/class B {public:virtual int f();};class D : public B {private:int f();};void f(){D d;B* pb = &d;D* pd = &d;pb->f(); //OK: B::f() is public,// D::f() is invokedpd->f(); //error: D::f() is private}/*—end example]Access is checked at the call point using the type of the expression used to denote the object for which the member function is called (B* in the example above). The access of the member function in the class in which it was defined (D in the example above) is in general not known.*/

    我们可以想像：当一个子类的虚成员函数通过基类的指针调用时，访问权限取决于基类对该函数的声明，而C++中private和proected仅仅是一个访问限定符，它只限定函数和数据不能被“直接”访问，而不担保这些函数和数据会被通过其他方法间接地访问到，在成员函数中返回一个类私有数据成员的引用，在外部就可以对这个私有属性进行修改（这个请参照博主的另一篇博客，对这个现象有说明）也是这个道理。