18-10.txt

《C/C++完美演绎》源代码

/* 范例：18-10 */
#include <iostream.h>
class A
{
  public:
    A():a(1){}
    virtual ~A(){}
    virtual void vf1(){cout << "A::vf1()\n";}
    int a;
};
class B:public A
{
  public:
    B():b(2){}
    virtual ~B(){}
    int b;
};
class C:public A
{
  public:
    C():c(3){}
    virtual ~C(){}
    int c;
};
class D:public C
{
  public:
    D():d(4){}
    virtual ~D(){}
    int d;
};
class F
{
  public:
    F():f(6){}
    virtual ~F(){}
    int f;
};

class E:public B,public D,public F
{
  public:
    E():e(5){}
    virtual ~E(){}
    int e;
};

void main()
{
  B *pb;
  C *pc;
  F *pf;

  pc = new D; 	// # 1
  pb = dynamic_cast<B*>(pc); 	// 失败
  if(pb)
    cout << "1st: " << pb->b << endl;
  delete pc;

  pc = new E;
  pb = dynamic_cast<B*>(pc);  	// 成功
  if(pb)
    cout << "2nd: " << pb->b << endl;
  delete pc;

  pc = new E;
  pf = dynamic_cast<F*>(pc);
  if(pf)
    cout << "3rd: " << pf->f << endl;
  delete pc;

  getchar();
}

程序执行结果：
2nd: 2
3rd: 6