C++多态

 1 //为时钟类重载单目运算符++和--
　　#define _CRT_SECURE_NO_WARNINGS
 2 
 3 #include <iostream>
 4 
 5 using namespace std;
 6 
 7 class Clock {//时钟类定义
 8 public:
 9     Clock(int hour = 0, int minute = 0, int second = 0);
10     void showTime() const;
11     //前置单目运算符重载
12     Clock& operator ++ ();
13     //后置单目运算符重载
14     Clock operator ++ (int);
15 private:
16     int hour, minute, second;
17 };
18 
19 Clock::Clock(int hour, int minute, int second)
20 {
21     if (0 <= hour && hour < 24 && 0 <= minute && minute < 60
22         && 0 <= second && second < 60) {
23         this->hour = hour;
24         this->minute = minute;
25         this->second = second;
26     }
27     else
28         cout << "Time error!" << endl;
29 }

30 void Clock::showTime() const
31 {  //显示时间
32     cout << hour << ":" << minute << ":" << second << endl;
33 }
34 
35 //前置返回当前对象，通过引用可以直接操作对象，所以是左值
36 Clock & Clock::operator ++ ()
37 {
38     second++;
39     if (second >= 60) {
40         second -= 60;  minute++;
41         if (minute >= 60) {
42             minute -= 60; hour = (hour + 1) % 24;
43         }
44     }
45     return *this;
46 }
47 
48 //后置，返回临时局部对象，不能通过该值改变对象，所以是右值
49 Clock Clock::operator ++ (int)
50 {
51     //注意形参表中的整型参数
52     Clock old = *this;
53     ++(*this);  //调用前置“++”运算符
54     return old;
55 }
56 
57 
58 int main()
59 {
60     Clock myClock(23, 59, 59);
61     cout << "First time output: ";
62     myClock.showTime();
63     cout << "Show myClock++:    ";
64     (myClock++).showTime();
65     cout << "Show ++myClock:    ";
66     (++myClock).showTime();
67 
68     return 0;
69 }

1 //为复数类重载加减法和"<<"运算符

 1 #define _CRT_SECURE_NO_WARNINGS
 2 
 3 #include <iostream>
 4 
 5 using namespace std;
 6 
 7 class Complex {
 8 public:
 9     Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {}
10     friend Complex operator+(const Complex &c1, const Complex &c2);
11     friend Complex operator-(const Complex &c1, const Complex &c2);
12     friend ostream & operator<<(ostream &out, const Complex &c);
13 private:
14     double real;  //复数实部
15     double imag;  //复数虚部
16 };
17 
18 
19 Complex operator+(const Complex &c1, const Complex &c2)
20 {
21     return Complex(c1.real + c2.real, c1.imag + c2.imag);
22 }
23 Complex operator-(const Complex &c1, const Complex &c2)
24 {
25     return Complex(c1.real - c2.real, c1.imag - c2.imag);
26 }
27 
28 //实现级联输出
29 ostream & operator<<(ostream &out, const Complex &c)
30 {
31     out << "(" << c.real << ", " << c.imag << ")";
32     return out;
33 }
34 
35 int main()
36 {
37     Complex c1(5, 4), c2(2, 10), c3;
38     cout << "c1 = " << c1 << endl;
39     cout << "c2 = " << c2 << endl;
40     c3 = c1 - c2;   //使用重载运算符完成复数减法
41     cout << "c3 = c1 - c2 = " << c3 << endl;
42     c3 = c1 + c2;   //使用重载运算符完成复数加法
43     cout << "c3 = c1 + c2 = " << c3 << endl;
44 
45     return 0;
46 }

 1 class Base {
 2 public:
 3     virtual void f();
 4     virtual void g();
 5 private:
 6     int i;
 7 };
 8 
 9 class Derived : public Base {
10 public:
11     virtual void f();  //覆盖Base::f
12     virtual void h();  //新增虚函数
13 private:
14     int j;
15 };