修改Example10~12，将类定义中的运算符重载都改用友元函数实现。

显然，需要对mytime3.h,mytime3.cpp做修改，而usetime3.cpp不需要修改。

程序清单如下：

---

// mytime4.h

#ifndef MYTIME3_H_

#define MYTIME3_H_

#include <iostream>

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);

    friend Time operator+(const Time& t1, const Time& t2);

    friend Time operator-(const Time& t1, const Time& t2);

    friend Time operator*(const Time& t, double n);

    friend Time operator*(double n, const Time& t);

    friend std::ostream& operator<<(std::ostream& os, const Time& t);

};

#endif

---

// mytime4.cpp

#include <iostream>

#include "mytime4.h"

Time::Time()

{

    hours = 0;

    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 operator+(const Time& t1, const Time& t2)

{

    Time sum;

    sum.minutes = t1.minutes + t2.minutes;

    sum.hours = t1.hours + t2.hours + sum.minutes / 60;

    sum.minutes %= 60;

    return sum;

}

Time operator-(const Time& t1, const Time& t2)

{

    Time diff;

    int tot1, tot2;

    tot1 = t1.hours * 60 + t1.minutes;

    tot2 = t1.hours * 60 + t1.minutes;

    diff.hours = (tot1 - tot2) / 60;

    diff.minutes = (tot1 -tot2) % 60;

    return diff;

}

Time operator*(const Time& t, double n)

{

    Time result;

    long totalminutes = t.hours * 60 * n + t.minutes * n;

    result.hours = totalminutes / 60;

    result.minutes = totalminutes % 60;

    return result;

}

Time operator*(double n, const Time& t)

{

    return t * n;

}

std::ostream& operator<<(std::ostream& os, const Time& t)

{

    os << t.hours << ":" << t.minutes;

    return os;

}

---

 

结束。