C++中虚函数指针问题

《Inside C++ model》中已经解释的很详细了，这篇文章http://blog.csdn.net/heavendai/article/details/7008066，解释了如何调用找出虚函数的地址并调用，后来我发现其实取出的函数指针并不能应用，因为没传递函数指针，所以如果虚函数中对成员变量的访问将会是未定义的行为，比较危险。我来实现一个比较实用的基类指针，用来指向虚函数，下面是demo：

#include <iostream>

using namespace std;

class Base {
public:
    typedef void (Base::*handler_ptr)();
    Base():x(3), y(4){}

    virtual void f() { cout << "Base::f" << endl; cout << "my x is " << x << endl;}

    virtual void g() { cout << "Base::g" << endl; }

    virtual void h() { cout << "Base::h" << endl; }

    int x;
    int y;
    handler_ptr ptr_;
};

class Derive : public Base
{
public:
    virtual void f() { cout << "Derive::f" << endl << "my x is " << x << endl;}
    virtual void h() { cout << "Derive::h" << endl << "my y is " << y << endl;}
    void test_h()
    {
        ptr_ = &Base::h;
        (this->*ptr_)(); 
    }
};


typedef void (Base::*fun_ptr)();

int main()
{
    Base b;
    fun_ptr pfun_my = &Base::f;
    (b.*pfun_my)();
    Derive d;
    (d.*pfun_my)();
    d.test_h();
    return 0;
}

这样，x和y的访问是没有问题的。

输出为

Base::f
my x is 3
Derive::f
my x is 3
Derive::h
my y is 4