在未构造的对象上调用成员函数，C ++

Question

因此：

class A 
{ 
public: 
    A() 
    { 
        cout << "A() "; 
    } 
    void f() 
    { 
        cout << "f "; 
    } 
    ~A() 
    { 
        cout << "~A() "; 
    } 
};

int  main()
{
    A *p = (A*)2; 
    p->f(); 
}
class A 
{ 
public: 
    A() 
    { 
        cout << "A() "; 
    } 
    void f() 
    { 
        cout << "f "; 
    } 
    ~A() 
    { 
        cout << "~A() "; 
    } 
};

int  main()
{
    A *p = (A*)2; 
    p->f(); 
}
//ouput is 
// f

程序如何调用非现有对象的成员函数？ 程序如何将this指针传递给函数？