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 0;
    }
};

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");
};