ATL布幔之下的秘密(2)

程序24.#include <iostream>
using namespace std;
class Base {
public:
　　Base() {
　　　　cout << "In Base" << endl;
　　　　cout << "Virtual Pointer = " << (int*)this << endl;
　　　　cout << "Address of Vtable = " << (int*)*(int*)this << endl;
　　　　cout << "Value at Vtable = " << (int*)*(int*)*(int*)this << endl;
　　　　cout << endl;
　　}
　　virtual void f1() { cout << "Base::f1" << endl; }
};
class Drive : public Base {
public:
　　Drive() {
　　　　cout << "In Drive" << endl;
　　　　cout << "Virtual Pointer = " << (int*)this << endl;
　　　　cout << "Address of Vtable = " << (int*)*(int*)this << endl;
　　　　cout << "Value at Vtable = " << (int*)*(int*)*(int*)this << endl;
　　　　cout << endl;
　　}
　　virtual void f1() { cout << "Drive::f2" << endl; }
};
class MostDrive : public Drive {
public:
　　MostDrive() {
　　　　cout << "In MostDrive" << endl;
　　　　cout << "Virtual Pointer = " << (int*)this << endl;
　　　　cout << "Address of Vtable = " << (int*)*(int*)this << endl;
　　　　cout << "Value at Vtable = " << (int*)*(int*)*(int*)this << endl;
　　　　cout << endl;
　　}
　　virtual void f1() { cout << "MostDrive::f2" << endl; }
};
int main() {
　　MostDrive d;
　　return 0;
}程序的输出为：In Base
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C0A0
Value at Vtable = 004010F5
In Drive
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C090
Value at Vtable = 00401221
In MostDrive
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C080
Value at Vtable = 00401186这个程序示范了虚函数表指针在每个类的构造函数中的初始化过程。这样看来，每个类构造函数中虚函数表的地址是不同的，main函数则使用了继承链中的最底部的派生类来创建对象。