通过我们对运算符重载的学习，我们可以由此实现一个日期类。

头文件：

#pragma once
#include<iostream>
#include<assert.h>
using std::endl;
using std::cout;
using std::cin;
using std::ostream;
using std::istream;class Date{//声明友元friend ostream& operator<<(ostream& out, Date& d1);friend istream& operator>>(istream& in, Date& d1);
public:// 全缺省的构造函数Date(int year=-1, int month=-1, int day=-1);// 拷贝构造函数// d2(d1)Date(const Date& da);// 析构函数~Date();//打印日期函数void Print();//判断日期是否合法bool DateCheck();// 赋值运算符重载// d2 = d3 -> d2.operator=(&d2, d3)Date& operator=(const Date&da);// 日期+=天数Date& operator+=(int day);// 日期+天数Date operator+(int day);// 日期-天数Date operator-(int day);// 日期-=天数Date& operator-=(int day);// 前置++Date& operator++();// 后置++Date operator++(int);// 后置--Date operator--(int);// 前置--Date& operator--();// >运算符重载bool operator>(const Date& d);// ==运算符重载bool operator==(const Date& d);// >=运算符重载bool operator >= (const Date& d);// <运算符重载bool operator < (const Date& d);// <=运算符重载bool operator <= (const Date& d);// !=运算符重载bool operator != (const Date& d);// 日期-日期 返回天数int operator-(const Date& d);void operator()(istream& in, Date& d1);private:int _year;int _month;int _day;};//流插入重载
ostream& operator<<(ostream& out, Date& d1);//流提取重载
istream& operator>>(istream& in, Date &d1);

函数实现文件：

#include"Date.h"// 获取某年某月的天数
int GetMonthDay(int year, int month)
{assert(month > 0 && month < 13);static  int arr[13] = { -1,31,28,31,30,31,30,31,31,30,31,30,31 };if (month == 2 && ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0))return arr[2] + 1;return arr[month];
}bool Date::DateCheck()
{if (_month <= 0 || _month > 12 ||_day<=0|| _day > GetMonthDay(_year, _month)){return false;}return true;
}// 全缺省的构造函数
Date::Date(int year, int month, int day)
{//cout << "Date::Date(int year, int month, int day)" << endl;_year = year;_month = month;_day = day;
}// 拷贝构造函数
// d2(d1)
Date::Date(const Date& da)  
{_day=da._day;_year=da._year ;_month=da._month ;
}Date::~Date()
{/*cout << "Date::~Date()" <<endl ;*/_year = -1;_day = -1;_month = -1;
}void Date::Print()
{cout << _year << " " << _month << " " << _day << " " << endl;
}// 赋值运算符重载
// d2 = d3 -> d2.operator=(&d2, d3)
Date& Date::operator=(const  Date& da)
{_year = da._year;_month = da._month;_day = da._day;return *this;
}// 日期+=天数Date& Date::operator+=(int day)
{_day += day;while (_day>GetMonthDay(_year,_month)){_day -= GetMonthDay(_year, _month);_month++;if (_month > 12){_year++;_month = 1;}}return *this;
}
// 日期+天数
Date Date::operator+(int day)
{Date temp = *this;temp += day;return temp;
}// 日期-天数
Date Date::operator-(int day)
{Date temp = *this;*this -= day;return *this;
}// 日期-=天数
Date& Date::operator-=(int day)
{_day -= day;while (_day <= 0){_month--;if (_month == 0){_month = 12;_year -= 1;}_day += GetMonthDay(_year, _month);}return *this;
}// 前置++Date& Date:: operator++()
{*this+= 1;return *this;
}// 后置++
Date Date::operator++(int)
{Date temp = *this;*this += 1;return temp;
}// 后置--
Date Date::operator--(int)
{Date temp = *this;*this -= 1;return temp;
}// 前置--Date& Date::operator--()
{*this -= 1;return *this;
}// >运算符重载bool Date::operator>(const Date& d)
{if (_year > d._year){return true;}else{if (_year == d._year){if (_month > d._month){return true;}else{if (_month == d._month){if (_day > d._day){return true;}}}}}return false;
}// ==运算符重载bool Date::operator==(const Date& d)
{if (_year == d._year && _month == d._month && _day == d._day){return true;}return false;
}// >=运算符重载bool Date::operator >= (const Date& d)
{if (*this > d || *this == d){return true;}return false;
}// <运算符重载bool Date::operator < (const Date& d)
{if (!(*this >= d)){return true;}return false;
}// <=运算符重载bool Date::operator <= (const Date& d)
{if (*this < d || *this == d){return true;}return false;
}// !=运算符重载bool Date::operator != (const Date& d)
{if (!(*this == d)){return true;}return false;
}// 日期-日期 返回天数int Date::operator-(const Date& d)
{int falg = 1;Date max =*this;Date min = d;if (*this < d){max = d;min = *this;falg = -1;}int n = 0;while (min < max){++min;n++;}return n * falg;
}//流提取
ostream& operator<<(ostream& out, Date&d1)
{out << d1._year << " " << d1._month << " " << d1._day << " " ;return cout;
}//流插入
istream& operator>>(istream& in, Date& d1)
{cout << "请输入合法日期喵~O(∩_∩)O" << endl;in >> d1._year >> d1._month >> d1._day;while(!d1.DateCheck()){cout << "日期不合法喵~/(ㄒoㄒ)/~~" << endl;cout << "请输入合法日期喵~o(=^ェ^=)m" << endl;in >> d1._year >> d1._month >> d1._day;}return in;
}

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