C++中使用类（重载，友元函数，转换函数等）

12点半了。好久没更新C++博文了。把一个章节看完了。接下来说下C++里的操作符重载和以后的内容。时间晚了，可能打字没打好。望大家见谅。
C++中有个operator操作符概念。如果想重载+运算符，那么需要写成operator+()。一般两个数相加是这么调用的：
[cpp]
a = b+c; == a = b.operator+(c);

当调用操作符，会有一个隐式的调用。把自己的对象作为操作符的对象。然后显示调用参数c。
重点介绍友元函数。因为重载了运算符后可能出现类似：
[cpp]
a = 1.5 + c;

此时按照上面的说法。1.5不是一个对象。无法完成操作，这时候就需要友元函数了，其实友元函数就是类的非成员函数，不会隐式的将自身对象也作为参数。
然后贴三段代码，注释写的还算详细。大家可以复制后去运行下看下结果。代码是从C++Primer Plus里抄过来的。
mytime0.h
[cpp]
#ifndef MYTIME0_H_
#define MYTIME0_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);
    Time Sum(const Time & t)const;
// 接下来时重载+运算符的函数
    Time operator+(const Time & t)const;
    void Show()const;
// 重载-运算符的函数
    Time operator-(const Time & t)const;
// 重载*运算符的函数
    Time operator*(double n)const;
// 友元函数类似 a+b 的原型是 a.operator+(b); 所以如果 5*a 则5没有那个重载的函数，这时就不能使用类的成员函数了，需要友元函数来进行操作，类友元函数也就是非成员函数
    friend Time operator*(double m, const Time & t){return t * m;} //内联函数，调用该类的成员函数，这里也就是上面那个函数。
// 友元函数。对于那些非成员重载操作符函数来说，操作符左面的操作数对应函数的第一个参数。类似 c = a+b 类似于 c = operator+(a,b)
    friend std::ostream & operator<<(std::ostream & os, const Time & t);
};

#endif
mytime0.cpp
[cpp]
#include <iostream>
#include "mytime0.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::Sum(const Time & t)const
{
    Time sum;
    sum.minutes = minutes + t.minutes;
    sum.hours = hours + t.hours + sum.minutes/60;
    sum.minutes %= 60;
    return sum;
}

// 重载加号运算符的版本
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 n)const
{
    Time result;
    long totalminutes = hours * n * 60 + minutes * n;
    result.hours = totalminutes / 60;
    result.minutes = totalminutes % 60;
    return result;
}

std::ostream & operator<<(std::ostream & os, const Time & t)
{
    os << t.hours << "hours, " << t.minutes << " minutes";
    return os;
}

void Time::Show()const
{
    std::cout << hours << " hours, " << minutes << " minutes";

}

//usetime0.cpp
#include <iostream>
#include "mytime0.h"

int main()
{
    using std::cout;
    using std::endl;
    Time planning;
    Time coding(2, 40);
    Time fixing(5, 55);
    Time total;

    cout << "planning time = ";
    planning.Show();
    cout << endl;

    cout << "coding time = ";
    coding.Show();
    cout << endl;

    cout << "fixing time = ";
    fixing.Show();
    cout << endl;

// total = coding.Sum(fixing);
// 重载加号运算符的版本
    total = coding + fixing;
    cout << "coding + fixing = ";
    total.Show();
    cout << endl;

    Time morefixing(3 ,20);
    cout << "more fixing time = ";
    morefixing.Show();
    cout << endl;
    total = morefixing.operator+(total);
    cout << "morefixing.operator+(total) = ";
    total.Show();
    cout << endl;

    Time aida(3, 35);
    Time tosca(2, 48);
    Time temp;

    cout << "Aida and TOsca:\n";
    cout << aida <<"; " << tosca << endl;
    temp = aida + tosca;        // operator+()
    cout << "Aida + Tosca: " << temp << endl;&

补充：软件开发 , C++ ,