class Person{public:    virtual void test(){ cout << __FUNCTION__ << endl;}};class Student : public Person{public:    virtual void test() { cout << __FUNCTION__ << endl;}};void test_virtual(Person * p){...}test_virtual(Student()) ; //没问题吧

但只在public 继承这才没问题 : Person * p = new Student

现在把 public 继承修改:

class Person{public:    virtual void test(){ cout << __FUNCTION__ << endl;}};class Student : protected Person{        //protected 继承public:    virtual void test() { cout << __FUNCTION__ << endl;}        //内部依然可以使用virtual函数    void test_virtual(){        Person * p = this;        p->test();    }};

现在呢 : Person p = new Student //conversion from 'Student ' to 'Person *' exists, but is inaccessible