运算符重载C++

Operator Overloading C++

本文关键字：C++ 重载 运算符      更新时间：2023-10-16

我正在尝试创建一个程序，该程序将要求用户输入一个月。然后程序将显示月份，下个月，上个月，后第五个月和前第七个月。我无法让程序减去一个月，或以下其他操作。我只能让它在下个月添加。有什么想法吗？

#include <iostream>
#include <string>
using namespace std;
enum Month { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC };
Month& operator++(Month& theMonth)
{
if (theMonth == DEC)
    theMonth = JAN;
else
    theMonth = static_cast<Month>(theMonth + 1); 
return theMonth;
}
Month& operator--(Month& theMonth)
{
if (theMonth == JAN)
    theMonth = DEC;
else
    theMonth = static_cast<Month>(theMonth - 1); 
return theMonth;
}
   ostream &operator<<(ostream &output, Month &theMonth)
{
switch (theMonth){
case JAN: output << "January";
    break;
case FEB: output << "February";
    break;
case MAR: output << "March";
    break;
case APR: output << "April";
    break;
case MAY: output << "May";
    break;
case JUN: output << "June";
    break;
case JUL: output << "July";
    break;
case AUG: output << "Augest";
    break;
case SEP: output << "September";
    break;
case OCT: output << "October";
    break;
case NOV: output << "November";
    break;
case DEC: output << "December";
    break;
}
return output;
}
istream &operator>>(istream &input, Month &theMonth)
{
int value;
input >> value;
theMonth = static_cast<Month>(value);
return input;
}


#include<iostream>
#include<string>
#include "Month.h"
using namespace std;
int main()
{
Month myMonth;
cout << "Enter Month (1-12): ";
cin >> myMonth;
cout << "You selected month, " << myMonth << " n" << endl;
cout << "The next month after the month you entered is " << myMonth++ <<     "n" << endl;
cout << "The month before the month you entered is " << myMonth-- << "n" <<  endl;
cout << "Five months after the month you entered is " << myMonth+= << "n"   << endl;
cout << "Seven months before the month you entered is " << myMonth-= << "n" << endl;
cin.ignore();
cin.get();
return 0;
}

我建议不要使用枚举值，而是使用一个不同的类，它包装一个 int：

class Month {
   int month_num; // Month, 0-11. (0-January, 1-February, etc...)
public:
   // ...
};

然后，所有的月份运算，如递增、递减、加n月、减去n月等等......——它们都变成了微不足道的模12算术。

显示月份名称也变得尽可能简单：

static const char * const months[] = {
   "January",
   "February",
   // etc... I'm too lazy to type
   "December"
};

那么，在实现std::ostream operator<<重载时，猜猜"月[month_num]"会为你做什么？

运算符++变为：

month_num=(month_num+1) % 12;

运算符 -- 变为

month_num=(month_num+11) % 12; // Yes, I just can't wrap negative values and modulo inside my brain, this is easier to grok...

运算符+=，将n添加到月份数字，变为

month_num=(month_num+n) % 12;

等。。。

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