关于C++操作符重载

[wxdcxp]

如何理解操作符左侧的对象是调用对象，操作符右侧对象是作为被参数传递对象？
另外如何理解这句： Total = Coding.sum(fixing)
以下代码摘自C++ primer 5th

// mytime0.cpp  -- implementing Time methods
#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;
}

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

// mytime0.h -- Time class before operator overloading
#ifndef MYTIME0_H_
#define MYTIME0_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 Sum(const Time & t) const;
    void Show() const;
};
#endif

// usetime0.cpp -- using the first draft of the Time class
// compile usetime0.cpp and mytime0.cpp together
#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);    cout << "coding.Sum(fixing) = ";
    total.Show();
    cout << endl;
   
    return 0;
}

[cphj]

total = coding.Sum(fixing);
C++编译器会翻译成类似这样：
total = Time_Sum(&coding, fixing);
&coding就是this指针的值,fixing的引用传给t
Sum函数计算完成之后返回值会复制给total对象


如何理解操作符左侧的对象是调用对象，操作符右侧对象是作为被参数传递对象？

例如A类重载了operator+(const A & a)
A a, b, c;
c = a + b;
C++编译器会翻译成类似这样：
C = A_operator+(&a, b);

[taodm]

嗯？C++ Primer第五版？
是时空穿越还是雕牌周住牌分不清？

[pengzhixi]

看看this指针那一节内容介绍

[wxdcxp]

感谢各位，不看object-oriented programming in c++这本书了，对this指针介绍的太少了。

[lnuyasha_hrb]

C++中的操作符是对对象而言的,一般操作符的重载发生在类或函数中.
如对于2目运算符来说，需要2个操作数,其中一个操作数是对象本身(this),而另一个操作数就是需要传递的参数

[illuminati]

如何理解操作符左侧的对象是调用对象，操作符右侧对象是作为被参数传递对象？
应该主要针对运算符重载而言
Total = Coding.sum(fixing)
无非就是调用coding对象的这个成员函数
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;
}