C++日期类（运算符的重载）

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日期类（运算符的重载）
在C++里可以实现运算符的重载，所以可以实现直接对日期类进行加减、比较等操作。
以下是整个Date.h头文件的源代码：
#pragma once#include<cassert>using namespace std;class Date{public:Date(int year = 1900, int month = 1, int day = 1):_year(year), _month(month), _day(day){assert(IsInvalid());    //判断日期是否合法}Date(const Date& d){_year = d._year;_month = d._month;_day = d._day;}~Date(){}void Display()     //打印日期类{cout << _year << "-" << _month << "-" << _day << endl;}bool IsInvalid()   //判断日期是否合法{if (_year >= 1900 && _month > 0 && _month < 13 && _day>0 && _day <= GetMonthDays(_year, _month)){return true;}return false;}int GetMonthDays(int year, int month)   //获取当前月份对应的天数{static int MonthDays[13] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };if (month != 2){return MonthDays[month];}else{if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))   //闰年{return 29;}return 28;}}Date operator+(int day);  //重载+Date& operator+=(int day);//重载++Date& operator++();    //前置++Date operator++(int);  //后置++Date operator-(int day);  //重载-Date& operator-=(int day);//重载-=Date& operator--();    //前置--Date operator--(int);  //后置--int operator-(const Date& d);   //两日期类对象相减返回一个整数bool operator>(const Date& d);  //重载>bool operator<(const Date& d);bool operator>=(const Date& d);bool operator<=(const Date& d);bool operator==(const Date& d);bool operator!=(const Date& d);private:int _year;int _month;int _day;};inline Date Date::operator+(int day){Date tmp(*this);if (day < 0){return *this - (-day);}tmp._day = _day + day;while (!tmp.IsInvalid()){int MonthDay = GetMonthDays(tmp._year, tmp._month);tmp._day -= MonthDay;tmp._month++;if (tmp._month == 13){tmp._year++;tmp._month = 1;}}return tmp;}inline Date&  Date::operator+=(int day){*this = *this + day;   //对加法重载的代码复用return *this;}inline Date&  Date::operator++()    //前置++{return *this+=1;}inline Date  Date::operator++(int)  //后置++{Date tmp(*this);*this += 1;return tmp;}inline Date Date::operator-(int day){Date tmp(*this);if (day < 0){return *this + (-day);}tmp._day = _day - day;while (!tmp.IsInvalid()){if (tmp._month != 1){tmp._month--;}else   //month==1的情况{tmp._year--;tmp._month = 12;}int MonthDay = GetMonthDays(tmp._year, tmp._month);tmp._day += MonthDay;}return tmp;}inline Date& Date::operator-=(int day){*this = *this - day;return *this;}inline Date& Date::operator--()    //前置--{return *this -= 1;}inline Date Date::operator--(int)  //后置--{Date tmp(*this);*this -= 1;return tmp;}inline bool Date::operator>(const Date& d){if (_year > d._year || (_year == d._year && (_month > d._month || (_month == d._month && _day > d._day)))){return true;}return false;}inline bool Date::operator<(const Date& d){return !(*this > d || *this == d);}inline bool Date::operator>=(const Date& d){return (*this > d || *this == d);}inline bool Date::operator<=(const Date& d){return (*this < d || *this == d);}inline bool Date::operator==(const Date& d){if (_year == d._year && _month == d._month && _day == d._day){return true;}return false;}inline bool Date::operator!=(const Date& d){return !(*this == d);}inline int Date::operator-(const Date& d)     //两日期类对象相减返回一个整数{int count = 0;Date tmp(*this);Date tmp2(d);if (tmp < tmp2)   //第一个日期比第二个小交换顺序{Date x;x = tmp;tmp = tmp2;tmp2 = x;}//处理_day使两个日期类的_day相同count = GetMonthDays(tmp2._year, tmp2._month) - tmp2._day + tmp._day;tmp2._day = tmp._day;if (tmp._day >= tmp2._day)  //count多加了一个月{tmp2._month++;if (tmp2._month == 13){tmp2._year++;tmp2._month = 1;}}//处理_month使两日期类_month相同while (tmp._month != tmp2._month){count = count + GetMonthDays(tmp2._year, tmp2._month);tmp2._month++;if (tmp2._month == 13) {tmp2._year++;tmp2._month = 1;}}//处理两日期类的_yearwhile (tmp._year > tmp2._year){//判断是否为闰年，并且在二月份一下的才能算366天if (((tmp2._year % 4 == 0 && tmp2._year % 100 != 0) || (tmp2._year % 400 == 0)) && (tmp2._month <= 2)){count += 366;}else{count += 365;}tmp2._year++;}return count;}
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