私有继承：派生类指针不能隐示的转换为基类指针

class base{
public:
virtual void display(){ cout << "base" << endl; }

};
class drive : private base{
public:
virtual void display(){ cout << "drive" << endl; }
};
int _tmain(int argc, _TCHAR* argv[])
{

//base* b = new drive; 　　　　//error

base* b = (base*)new drive; //right
b->display();　　　　　　　　//drive

}