C++取虚函数指针

#include <string>
#include <iostream>

//using namespace std;
using std::string;
using std::cout;
using std::endl;

class A
{
public:
    A(){};
    ~A(){};

    virtual void show1() { cout << "Ashow1" << endl; }
    virtual void show2() { cout << "Ashow2" << endl; }
    virtual void show3() { cout << "Ashow3" << endl; }
};


class B :public A
{
public:
    B(){};
    ~B(){};

    virtual void show1() { cout << "Bshow1" << endl; }
    virtual void show2() { cout << "Bshow2" << endl; }

};

typedef void(*pfun)();

int _tmain(int argc, _TCHAR* argv[])
{
    int len = sizeof(B);

    B* pObj = new B;
    pfun pf = NULL;

    /*
    (long*)bp，将对象的指针类型转换为(long*)类型，用于取出虚函数表的地址．
    *(long*)bp，*为取出指针指向的值．此式子即虚函数表的地址，也就是第一个虚函数的地址．
    (long*)*(long*)bp，将虚函数表的地址指针转换为(long*)，用于后续迭代．
    *(long*)*(long*)bp，＊求指针值，即为第一个虚函数的地址，最后转换为pfun指针.
    */
    for (int i = 0; i < 5;i++)
    {

        pf = (pfun)*((long*)*(long*)pObj + i);
        if (pf != 0)
        {
            pf();
        }

    }
    return 0;
}