04737_C++程序设计_第8章_多态性和虚函数

例8.1

分析下面程序的输出结果。

例8.2

分别使用指针和引用的display函数。

 #include <iostream>

 using namespace std;

 const double PI = 3.14159;

 class Point
 {
 private:
     double x, y;
 public:
     Point(double i, double j)
     {
         x = i;
         y = j;
     }
     virtual double area()
     {
         return ;
     }
 };

 class Circle :public Point
 {
 private:
     double radius;
 public:
     Circle(double a, double b, double r) :Point(a, b)
     {
         radius = r;
     }
     double area()
     {
         return PI*radius*radius;
     }
 };

 void display(Point *p)
 {
     cout << p->area() << endl;
 }

 void display(Point&a)
 {
     cout << a.area() << endl;
 }

 void main()
 {
     Point a(1.5, 6.7);
     Circle c(1.5, 6.7, 2.5);

     Point *p = &c;
     Point &rc = c;

     display(a);
     display(p);
     display(rc);

     system("pause");
 };

例8.3

在构造函数和析构函数中调用虚函数。

 #include <iostream>

 using namespace std;

 class A
 {
 public:
     A()
     {

     }
     virtual void func()
     {
         cout << "Constructing A" << endl;
     }
     ~A()
     {

     }
     virtual void fund()
     {
         cout << "Destructor A" << endl;
     }
 };

 class B :public A
 {
 public:
     B()
     {
         func();
     }
     void fun()
     {
         cout << "Come here and go...";
         func();
     }
     ~B()
     {
         fund();
     }
 };

 class C :public B
 {
 public:
     C()
     {

     }
     void func()
     {
         cout << "Class C" << endl;
     }
     ~C()
     {
         fund();
     }
     void fund()
     {
         cout << "Destructor C" << endl;
     }
 };

 void main()
 {
     C c;
     c.fun();

     system("pause");
 };

例8.5

多重继承使用虚函数。

 #include <iostream>

 using namespace std;

 class A
 {
 public:
     virtual void f()
     {
         cout << "Call A" << endl;
     }
 };

 class B
 {
 public:
     virtual void f()
     {
         cout << "Call B" << endl;//必须使用virtual声明
     }
 };

 class C :public A, public B
 {
 public:
     void f()//可以省略关键字virtual
     {
         cout << "Call C" << endl;
     }
 };

 void main()
 {
     A *pa;
     B *pb;
     C *pc, c;

     pa = &c;
     pb = &c;
     pc = &c;

     pa->f();//输出Call C
     pb->f();//输出Call C
     pc->f();//输出Call C

     system("pause");
 };