【C++】类和对象之日期类的实现（构造、运算符重载）

一、日期类要实现的函数

类名为Date

bool CheckDate(); //检查所用日期是否合法（有无越界）Date(int year = 1, int month = 1, int day = 1);//全缺省构造函数(初始化)Date(const Date& d);  //拷贝构造int GetMonthDay(int year, int month);//获取某年某月的天数void Print() const;//打印日期//运算符重载Date& operator+=(int day);
Date operator+(int day) const;// 加const后第一个参数变为了const Date* const this （第一个const)，this指向的内容就不能被改变
Date& operator-=(int day);
Date operator-(int day) const;//++d1(前置加加)
Date operator++();
//d1++（后置加加）为了区分前置和后置加加，规定后置加加要有形参
Date operator++(int);
//--d1
Date operator--();
//d1--
Date operator--(int);
//d1-d2
int operator-(const Date& d) const;//比较
bool operator<(const Date& d) const;
bool operator==(const Date& d) const;
bool operator!=(const Date& d) const;
bool operator<=(const Date& d) const;
bool operator>=(const Date& d) const;
bool operator>(const Date& d) const;//流插入
ostream& operator<<(ostream& out, const Date& d);
//流提取
istream& operator>>(istream& in, Date& d);

二、函数实现

若函数写在类的外面，要在函数名前面加 类名：：，在Date类中，为Date::

1、GetMonthDay获取对应月份的天数

//获取某年某月的天数
int GetMonthDay(int year, int month)
{	//断言，确保月份合法	assert(month > 0 && month < 13);//下标对应月份                      1  2 3  4  5  6  7  8  9  10 11 12static int getmonthDay[13] = { -1,31,28,31,30,31,30,31,31,30,31,30,31 };  //因为该函数（GetMonthDay）会被频繁调用，即会频繁创建数组，将数组放在静态区（static）更好//闰年二月有29天if (month == 2 && ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0))return 29;return getmonthDay[month];
}

2、CheckDate检查日期

判断month是否在1~12之间，以及该月对应的天数是否符合

//检查传的日期是否正确
bool Date::CheckDate()
{if (_month < 1 || _month>12 || _day <1 || _day>GetMonthDay(_year, _month))return false;elsereturn true;
}

3、Date构造函数

//全缺省构造
Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckDate()){cout << "非法日期：" << endl;Print();}}//拷贝构造
Date::Date(const Date& d)
{//将d拷贝给要构造的对象_year = d._year;_month = d._month;_day = d._day;
}

4、Print打印日期

void Date::Print() const
{cout << _year << "/" << _month << "/" << _day << endl;
}

5、运算符重载

1. += 、+、-=、-

//d1+=day（将d1直接改变了）
Date& Date::operator+=(int day)
{//day可能为负if (day < 0){return *this -= (-day);}_day += day;while (_day > GetMonthDay(_year, _month)){_day -= GetMonthDay(_year, _month);_month++;if (_month == 13){_month = 1;_year ++;}}return *this;
}//d1+day（d1的值不变）
Date Date::operator+(int day) const
{Date tmp = *this;//拷贝构造tmp += day;return tmp;
}//d1-=day(d1被改变了）
Date& Date::operator-=(int day)
{//day可能为负if (day < 0){return *this += (-day);}//用-=复用-//*this = *this-day;//return *this;_day -= day;while (_day <= 0) //_day>0合法{_month--;//_month为1月if (_month == 0){_month = 12;_year--;}_day += GetMonthDay(_year, _month);}return *this;
}
//d1-day（d1不变）
Date Date::operator-(int day) const
{Date tmp = *this;tmp -= day;return tmp;
}

2. 前置++/–、后置++/–

//++d1（表达式++d1的值改变，但d1自增）
Date Date::operator++()
{*this += 1;return *this;
}
//d1++（表达式d1++的值不变，但d1自增）
Date Date::operator++(int)
{Date tmp = *this;*this += 1;return tmp; //表达式的值不变，但d1自增
}Date Date::operator--()
{*this -= 1;return *this;
}
Date Date::operator--(int)
{Date tmp = *this;*this -= 1;return tmp;
}

3. 两个日期类相减（求相差日期）

//d1-d2
int Date::operator-(const Date& d)const
{int n = 0;int flag = 1;Date max = *this;Date min = d;if (*this < d){max = d;min = *this;flag = -1;}while (min != max){++min; ++n;}return n * flag;  //如果d1>d2 ,flag=1,天数相差为正数//如果d1<d2 ,flag=-1,天数相差为负数
}

6、比较

//写两个比较运算符重载，剩下的都可以通过复用这两个来完成
bool Date::operator<(const Date& d)const
{if (_year < d._year){return true;}else if (_year == d._year){if (_month < d._month)return true;else if (_month == d._month)return _day < d._day;}return false;//剩下的全为false
}
bool Date::operator==(const Date& d)const
{return _year == d._year && _month == d._month && _day == d._day;
}bool Date::operator<=(const Date& d)const
{ // d1<=d2  即 *this<=dreturn *this < d || *this == d;
}
bool Date::operator>(const Date& d)const
{return !(*this <= d);
}
bool Date::operator>=(const Date& d)const
{return *this > d || *this == d;
}
bool Date::operator!=(const Date& d)const
{return  _year != d._year || _month != d._month || _day != d._day;
}

7、流插入、流提取（输入输出）

若重载函数写在类的外面，要在类中加入友元函数声明，使其可以访问类的成员变量（private）

//友元函数声明
friend ostream& operator<<(ostream& out, const Date& d);
friend istream& operator>>(istream& in, Date& d);

//流插入
ostream& operator<<(ostream& out, const Date& d)
{out << d._year << "年" << d._month << "月" << d._day << "日" << endl; return out;//能够连续打印
}    //cout << d1 << d2;流插入是从左往右赋值//返回out后，相当于将cout<<d1变为了out，此时，变为了out<<d2 ，进而将d2打印出来了！//流提取
istream& operator>>(istream& in, Date& d)
{有非法日期时无法判断//cout << "请依次输入年月日：>";//in >> d._year >> d._month >> d._day;while (1){cout << "请依次输入年月日:>";in >> d._year >> d._month >> d._day;if (!d.CheckDate()){cout << "该输入日期非法：";d.Print();cout << "请重新输入！！！" << endl;}elsebreak;}return in;
}

三、完整代码

#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<assert.h>
using namespace std;class Date
{//友元函数声明friend ostream& operator<<(ostream& out, const Date& d);friend istream& operator>>(istream& in, Date& d);
public:bool CheckDate();//全缺省构造函数Date(int year = 1, int month = 1, int day = 1);//打印void Print() const;//拷贝构造Date(const Date& d);//获取某年某月的天数(直接在头文件中写，默认是内联函数inline)int GetMonthDay(int year, int month){		assert(month > 0 && month < 13);//下标对应月份                      1  2 3  4  5  6  7  8  9  10 11 12static int getmonthDay[13] = { -1,31,28,31,30,31,30,31,31,30,31,30,31 };  //因为该函数会被频繁调用，即会频繁创建数组，要放在静态区更好static//闰年二月有29天if (month == 2 && ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0))return 29;return getmonthDay[month];}//日期的加、减Date& operator+=(int day);Date operator+(int day) const;// 加const后第一个参数变为了const Date* const this （第一个const)，this指向的内容就不能被改变Date& operator-=(int day);Date operator-(int day) const;//比较bool operator<(const Date& d) const;bool operator==(const Date& d) const;bool operator!=(const Date& d) const;bool operator<=(const Date& d) const;bool operator>=(const Date& d) const;bool operator>(const Date& d) const;//前/后置 ++//后置++增加一个int形参(实际上编译器并不接收该形参)，与前置++构成函数重载//++d1Date operator++();//d1++Date operator++(int);Date operator--();Date operator--(int);//d1-d2int operator-(const Date& d) const;//流插入运算符重载  ，不符合用户习惯//void operator<<(ostream& out); 
private:int _year;int _month;int _day;};//检查传的日期是否正确
bool Date::CheckDate()
{if (_month < 1 || _month>12 || _day <1 || _day>GetMonthDay(_year, _month))return false;elsereturn true;
}
//全缺省构造
Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckDate()){cout << "非法日期：" << endl;Print();}}
//拷贝构造
Date::Date(const Date& d)
{//将d拷贝给要构造的对象_year = d._year;_month = d._month;_day = d._day;
}void Date::Print() const
{cout << _year << "/" << _month << "/" << _day << endl;
}//d1+=day（将d1直接改变了）
Date& Date::operator+=(int day)
{//day可能为负if (day < 0){return *this -= (-day);}_day += day;while (_day > GetMonthDay(_year, _month)){_day -= GetMonthDay(_year, _month);_month++;if (_month == 13){_month = 1;_year ++;}}return *this;
}//d1+day（这里的d1不变）
Date Date::operator+(int day) const
{Date tmp = *this;//拷贝构造tmp += day;return tmp;
}Date& Date::operator-=(int day)
{//day可能为负if (day < 0){return *this += (-day);}//用-=复用-//*this = *this-day;//return *this;_day -= day;while (_day <= 0) //_day>0合法{_month--;//_month为1月if (_month == 0){_month = 12;_year--;}_day += GetMonthDay(_year, _month);}return *this;
}
Date Date::operator-(int day) const
{Date tmp = *this;tmp -= day;return tmp;
}bool Date::operator<(const Date& d)const
{if (_year < d._year){return true;}else if (_year == d._year){if (_month < d._month)return true;else if (_month == d._month)return _day < d._day;}return false;//剩下的全为false
}
bool Date::operator==(const Date& d)const
{return _year == d._year && _month == d._month && _day == d._day;
}
bool Date::operator!=(const Date& d)const
{return  _year != d._year || _month != d._month || _day != d._day;
}
bool Date::operator<=(const Date& d)const
{ // d1<=d2  即 *this<=dreturn *this < d || *this == d;
}
bool Date::operator>(const Date& d)const
{return !(*this <= d);
}
bool Date::operator>=(const Date& d)const
{return *this > d || *this == d;
}//++d1
Date Date::operator++()
{*this += 1;return *this;
}
//d1++
Date Date::operator++(int)
{Date tmp = *this;*this += 1;return tmp; //表达式的值不变，但d1自增
}
Date Date::operator--()
{*this -= 1;return *this;
}
Date Date::operator--(int)
{Date tmp = *this;*this -= 1;return tmp;
}//d1-d2
int Date::operator-(const Date& d)const
{int n = 0;int flag = 1;Date max = *this;Date min = d;if (*this < d){max = d;min = *this;flag = -1;}while (min != max){++min; ++n;}return n * flag;  //如果d1>d2 ,flag=1,天数相差为正数//如果d1<d2 ,flag=-1,天数相差为负数
}//void Date::operator<<(ostream& out)
//{
//	out << _year << "年" << _month << "月" << _day << "日" << endl;
//}ostream& operator<<(ostream& out, const Date& d)
{out << d._year << "年" << d._month << "月" << d._day << "日" << endl; return out;//能够连续打印
}    //cout << d1 << d2;流插入是从左往右赋值//返回out后，相当于将cout<<d1变为了out，此时，变为了out<<d2 ，进而将d2打印出来了！
istream& operator>>(istream& in, Date& d)
{有非法日期时无法判断//cout << "请依次输入年月日：>";//in >> d._year >> d._month >> d._day;while (1){cout << "请依次输入年月日:>";in >> d._year >> d._month >> d._day;if (!d.CheckDate()){cout << "该输入日期非法：";d.Print();cout << "请重新输入！！！" << endl;}elsebreak;}return in;
}//测试
//成员函数的const要放到参数列表的后面
void Test01()
{  //+= 、 +Date a(2025, 4, 13);Date tmp = a + 100;  //或 Date tmp(a+100);a.Print();tmp.Print();a += 10000;a.Print();
}
void Test02()
{  //-= 、 -Date a(2025, 4, 14);a -= 100;a.Print();
}void Test03()
{Date a(2025, 4, 14);Date b(2024, 4, 14);cout << (a < b) << endl;
}void Test04()
{Date a(2025, 4, 14);/*Date tmp1 = a++;a.Print();tmp1.Print();*/Date tmp2 = ++a;  // a.operator++();a.Print();tmp2.Print();
}void Test05()
{   //a、b相差多少天Date a(2025, 4, 15);Date b(2024, 4, 31);cout << (a - b) << endl;
}void Test06()
{Date d1;Date d2;//cout<<d1;//d1 << cout;//void operator<<(ostream & out); 参数列表有一个隐含的this指针，this为第一个参数，而out为第二个，故传参的时候，要将d1写在前面//cout << d1 << d2;//有return可以实现连续打印cin >> d1 >> d2;cout << d1 - d2 << endl;
}
int main()
{//Test01();//Test02();//Test03();Test06();return 0;
}

三、谢谢观看！