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运算符重载的限制：

限制这么多 人生还有什么意义= =python倒是可以把+变- -变*之类的

示例代码：

mytime2.h

#ifndef MYTIME2_H_#define MYTIME2_H_class Time{  private:    int hours;    int minutes;  public:    Time();    Time(int h, int m = 0);    void AddMin(int m);    void AddHr(int h);    void Reset(int h = 0, int m = 0);    Time operator+ (const Time & t) const;    Time operator- (const Time & t) const;    Time operator* (double n) const;    void Show() const;};#endif

mytime2.cpp

#include 
   
    #include "mytime2.h"Time::Time(){  hours = minutes = 0;  }Time::Time(int h, int m){  hours = h;  minutes = m;}void Time::AddMin(int m){  minutes = m;  hours += minutes / 60;  minutes %= 60;}void Time::AddHr(int h){  hours += h;}void Time::Reset(int h, int m){  hours = h;  minutes = m;}Time Time::operator+ (const Time & t) const{  Time sum;  sum.minutes = minutes + t.minutes;  sum.hours = hours + t.hours + sum.minutes / 60;  sum.minutes %= 60;  return sum;}Time Time::operator- (const Time & t) const{  Time diff;  int tot1, tot2;  tot1 = t.minutes + 60 * t.hours;  tot2 = minutes + 60 * hours;  diff.minutes = (tot2 -tot1 ) % 60;  diff.hours = (tot2 - tot1) / 60;  return diff;}Time Time::operator* (double mult) const{  Time result;  long totalminutes = hours * mult * 60 + minutes * mult;  result.hours = totalminutes / 60;  result.minutes = totalminutes % 60;  return result;}void Time::Show() const{  std::cout << hours << " hours, " << minutes << " minutes";}
   

usetime2.cpp

#include 
   
    #include "mytime2.h"int main(){  using std::cout;  using std::endl;  Time weeding(4, 35);  Time waxing(2, 47);  Time total;  Time diff;  Time adjusted;  cout << "weeding time = ";  weeding.Show();  cout << endl;  cout << "waxing time = ";  waxing.Show();  cout << endl; cout << "total work time = ";  total = weeding + waxing;  total.Show();  cout << endl;  diff = weeding - waxing;  cout << "weeding time - waxing time = ";  diff.Show();  cout << endl;  adjusted = total * 1.5;  cout << "adjusted work time = ";  adjusted.Show();  cout << endl;  return 0;}
   

友元（有缘= =）

友元函数

友元类

友元成员函数

处理外部函数调用类私有函数或对象 

比如 Time * 1.5 改成 1.5 * Time

一般情况 Time::Time operator* (double n)  const

这样的话就没办法适用1.5 * Time

所以需要友元函数来跟Time对象做做关系，让外部函数能够访问Time对象的成员函数或对象

  关于<< 的重载

这种方法只能适用于简单的 cout << time;

但是如果碰到 cout << "abc" << time 就没用了

那咋办捏 

这样写：

ostream & operator<< (ostream & os, Time & t)

{

.......

  return os;

}

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