C++改变虚指针指向的虚表

#include <iostream>

using namespace std;

class A
{
public:
A():m_a(1){}
int m_a;
virtual void f(){ cout << "A   fun "<<m_a << endl; };
};

class B
{
public:
B() :m_b(2){}
int m_b;
virtual void f(){ cout << "B  fun " <<m_b<< endl; };
};

class C
{
public:
C():m_c(3){}
int m_c;
void f(){ cout << "C fun " << m_c << endl; }
};

class D : public C
{
public:
D():m_d(4){}
int m_d;
void f(){
cout << "D fun " << m_d << endl;
}
};

int main()
{
A* a = new A;
a->f();
cout << sizeof(a) << endl;
/*B* b = dynamic_cast<B*>(a);
if (b)
{
cout << "b is not null" << endl;
}
else
{
cout << "b is null" << endl;
}*/

int* vptr = reinterpret_cast<int*>(a);
cout <<hex<< *vptr << endl;

B* bb = static_cast<B*>(static_cast<void*>(a));
bb->f();
cout <<hex <<*vptr << endl;

B* b1 = new B;
b1->f();

*vptr = *reinterpret_cast<int*>(b1);//改变a对象的虚指针地址，指向b1的虚表

bb = static_cast<B*>(static_cast<void*>(a));
bb->f();

/*C* c = new D;
c->f();
D* d = static_cast<D*>(c);
d->f();*/
/*D* dd = dynamic_cast<D*>(c);
dd->f();*/

/*C* c = new C;
c->f();
D* d = static_cast<D*>(c);
d->f();*/

return 0;
}