/* 范例：17-9 */
#include <iostream.h>
class A   	// 父類
{
  public:
    A(int k):a(k){}
    int a;
};
class B:public A  	// 子類
{
  public:
    B(int i,int j):A(i),b(j){}
    int b;
};
void main()
{
  A obj_a(1);
  A *ptr_a = &obj_a;	// 建立一個(gè)ptr_a的對(duì)象指針指向obj_a對(duì)象
  B obj_b(2,3);
  B *ptr_b; 

  cout << "obj_a.a = " << obj_a.a << "\n";
  cout << "ptr_a 指向 obj_a => ptr_a->a = " << ptr_a->a << "\n";

  ptr_a = &obj_b;	// ok 自動(dòng)類型轉(zhuǎn)換    #1  // 圖解一
  //  ptr_a = (A*)&obj_b;	// ok 強(qiáng)迫類型轉(zhuǎn)換    #2  // 圖解二
  cout << "obj_b.a = " << obj_b.a << "\n";
  cout << "ptr_a 指向 obj_b => ptr_a->a = " << ptr_a->a << "\n";
  //  ptr_b = &obj_a;	// error 不會(huì)自動(dòng)轉(zhuǎn)型   #3
  ptr_b = (B*)&obj_a;	// ok,但危險(xiǎn)      #4  // 圖解三
  cout << ptr_b->a << "\n";
  cout << ptr_b->b << "\n";	// ???    #5

  getchar();
}

程序執(zhí)行結(jié)果：
obj_a.a = 1
ptr_a 指向 obj_a => ptr_a->a = 1
obj_b.a = 2
ptr_a 指向 obj_b => ptr_a->a = 2
1
6684208