ATL布幔之下的秘密(2)

程序32. #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 1st entry = " << (int*)*((int*)*(int*)this+0) << endl;
　　　　cout << "Value at Vtable 2nd entry = " << (int*)*((int*)*(int*)this+1) << endl;
　　　　cout << endl;
　　}
　　virtual void f1() = 0;
　　virtual void f2() = 0;
};
class __declspec(novtable) 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 1st entry = " << (int*)*((int*)*(int*)this+0) << endl;
　　　　cout << "Value at Vtable 2nd entry = " << (int*)*((int*)*(int*)this+1) << endl;
　　　　cout << endl;
　　}
};
class __declspec(novtable) 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 1st entry = " << (int*)*((int*)*(int*)this+0) << endl;
　　　　cout << "Value at Vtable 2nd entry = " << (int*)*((int*)*(int*)this+1) << endl;
　　　　cout << endl;
　　}
　　virtual void f1() { cout << "MostDrive::f1" << endl; }
　　virtual void f2() { cout << "MostDrive::f2" << endl; }
};
int main() {
　　MostDrive d;
　　return 0;
}
　　现在，程序的输出为：In Base
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C0C0
Value at Vtable 1st entry = 00420E50
Value at Vtable 2nd entry = 00420E50
In Drive
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C0C0
Value at Vtable 1st entry = 00420E50
Value at Vtable 2nd entry = 00420E50
In MostDrive
Virtual Pointer = 0012FF7C
Address of Vtable = 0046C0C0
Value at Vtable 1st entry = 00420E50
Value at Vtable 2nd entry = 00420E50在MSDN中，对__declspec(novtable)的解释是：它应该使用在纯虚类中。那么，让我们再做一个实验来更好地弄懂这一含义吧。