在咱们刚接触C++,写一个日期类进行练习，实现从能比较多，如计算日期差，设置日期，输出日期…
下面我会展示一个简单的日期类

声明

#include <iostream>
#include <assert.h>
using namespace std;class Date
{
public:bool CheckInvalid();Date(int year = 1, int month = 1, int day = 1);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);bool operator!=(const Date&d);// 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);//频繁调用直接写内联函数int GetMonthDay(int year, int month){assert(month > 0 && month < 13);static int monthDays[13] = { 0, 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 29;}return monthDays[month];}void Print(){cout << _year << "/" << _month << "/" << _day << endl;}//友元声明friend ostream& operator<<(ostream& out, const Date& d);friend istream& operator>>(istream& in, Date& d);private:int _year;int _month;int _day;
};ostream& operator<<(ostream& out, const Date& d);
istream& operator>>(istream& in,Date& d);

主体程序

#include "Date.h"Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckInvalid()){cout << "日期非法" << endl;}
}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;
}bool Date::operator<=(const Date&d)
{return *this < d || *this == d;
}bool Date::operator>(const Date&d)
{return !(*this <= d);
}bool Date::operator>=(const Date&d)
{return !(*this < d);
}bool Date::operator==(const Date&d)
{return _year  == d._year&&_month == d._month&&_day   == d._day;
}bool Date::operator!=(const Date&d)
{return !(*this == d);
}Date& Date::operator+= (int day)
{_day += day;while (_day > GetMonthDay(_year, _month)){_day -= GetMonthDay(_year,_month);++_month;if (_month == 13){++_year;_month = 1;}}return *this;
}Date Date::operator+ (int day)
{//这两种都是拷贝构造//Date tmp(*this);Date tmp = *this;tmp += day;return tmp;//这里我就重载了，下面就注释了//tmp._day += day;//while (tmp._day > GetMonthDay(tmp._year, tmp._month))//{//	tmp._day -= GetMonthDay(tmp._year, tmp._month);//	++tmp._month;//	if (_month == 13)//	{//		++tmp._year;//		tmp._month = 1;//	}//}////return tmp;
}Date& Date::operator-= (int day)
{_day -= day;while (_day <= 0){--_month;if (_month == 0){_year--;_month = 12;}_day += GetMonthDay(_year, _month);}return *this;
}Date Date::operator- (int day)
{Date tmp = *this;tmp -= day;return tmp;
}bool Date::CheckInvalid()
{if (_year <= 0 || _month<1 || _month>12 || _day<1 || _day>GetMonthDay(_year, _month)){return false;}else{return true;}
}ostream& operator<<(ostream& out, const Date& d)
{out << d._year << "年" << d._month << "月" << d._day << "日" << endl;return out;//要返回值是要连续流提取/插入
}istream& operator>>(istream& in, Date& d)
{while (1){cout << "输入日期：";in >> d._year >> d._month >> d._day;if (!d.CheckInvalid()){cout << "日期非法" << endl;}else{break;}}return in;//要返回值是要连续流提取/插入
}

测试和应用

加天数后的日期

#include "Date.h"int main()
{Date d1(2024, 1, 29);Date d2 = d1 + 20;d2.Print();d1.Print();return 0;
}

用流来进行提取和插入

#include "Date.h"int main()
{Date d1;Date d2;//函数重载，this指针是第一个参数，Date必须是左参数了operator<<(cout,d1);cin >> d2>>d1;cout << d2 << d1;return 0;
}