日期类的实现，const成员

一：日期类实现

//头文件

#include <iostream>
using namespace std;

class Date
{
	friend ostream& operator<<(ostream& out, const Date d);
	friend istream& operator>>(istream& in, const Date d);
public:
	Date(int year = 1900, int month = 1, int day = 1);

	void Print()
	{
		cout << "年 " << _year << "月 " << _month<<"日 " << _day << endl;
	}

	//得到对应年月的天数
	int GetMonthDay(int year, int month)
	{
		static int day[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };

		if(month == 2 &&((year%100 != 0&& year%4==0) || (year % 400 == 0)))
			return day[month]+1;
		else
			return day[month];
	}

	bool CheckDay();

	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;

	Date& operator+=(int day);
	Date operator+(int day);

	Date& operator-=(int day);
	Date operator-(int day);

	Date operator++();
	Date operator++(int);

	Date operator--();
	Date operator--(int);

	int operator-(const Date d);

private:
	int _year;
	int _month;
	int _day;
};

ostream& operator<<(ostream& out, const Date d);
istream& operator>>(istream& in, const Date d);

//实现

#include "Date.h"

Date::Date(int year, int month, int day)
{
	_year = year;
	_month = month;
	_day = day;
}

bool Date::CheckDay()
{
	if (_month > 12 || _month < 0 || _day <0 || _day > GetMonthDay(_year, _month))
		return false;
	else
		return true;

}

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;
}

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;

}

bool Date::operator>=(const Date d)const
{
	return ((*this) > d) || ((*this) == d);
}

bool Date::operator>(const Date d)const
{
	return !((*this) <= d);
}

bool Date::operator!=(const Date d)const
{
	return !((*this) == d);
}


Date& Date::operator+=(int day)
{
	if (day < 0)
		return (*this) -= -day;

	_day += day;
	while (_day > GetMonthDay(_year, _month))
	{
		_day -= GetMonthDay(_year, _month);
		_month++;

		if (_month > 12)
		{
			_year++;
			_month = 1;
		}
	}

	return (*this);
}
Date Date::operator+(int day)
{
	Date tmp = *this;
	tmp += day;

	return tmp;
}


Date& Date::operator-=(int day)
{
	if (day < 0)
		return (*this) += -day;

	_day -= day;

	while (_day <= 0)
	{
		if (_month--  < 1)
		{
			_month = 12;
			_year--;
		}

		_day += GetMonthDay(_year, _month);
	}

	return (*this);
}
Date Date::operator-(int day)
{
	Date tmp = *this;
	tmp -= day;

	return tmp;
}

Date Date::operator++()
{

	return (*this) += 1;
}
Date Date::operator++(int)
{
	Date tmp = *this;
	*this += 1;

	return tmp;
}

Date Date::operator--()
{
	*this -= 1;
	return *this;
}
Date Date::operator--(int)
{
	Date tmp = *this;
	*this -= 1;
	return tmp;
}

int Date::operator-(const Date d)
{
	int flag = 1;
	int n = 0;
	//假设d1 大， d2小
	Date d1 = *this;
	Date d2 = d;

	if (d1 < d2)
	{
		flag = -1;
		d1 = d;
		d2 = *this;
	}

	while (d1 != d2)
	{
		n++;
		d2++;
	}

	return n * flag;
}

ostream& operator<<(ostream& out, const Date d)
{
	out << "年 " << d._year << "月 " << d._month << "日 " << d._day << endl;

	return out;
}

istream& operator>>(istream& in, const Date d)
{
	cout << "请输入年月日->";

	in >> d._year >> d._month >> d._day;
	
	return in;
}

二：const成员

将 const 修饰的 " 成员函数 " 称之为 const 成员函数 ， const 修饰类成员函数，实际修饰该成员函数
隐含的 this 指针，表明在该成员函数中 不能对类的任何成员进行修改。

class Date
{
public:
	Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}

	//void Print(Date* const this)  本身指向的对象是不能修改的，但是指向的内容可以改 
	void Print()
	{
		cout << "年" << _year << endl;
		cout << "月" << _month << endl;
		cout << "日" << _day << endl;
	}

	//void Print(const Date* const this)  本身指向的对象 和 指向的对象的内容 都不可以修改
	void Print()const
	{
		cout << "年" << _year << endl;
		cout << "月" << _month << endl;
		cout << "日" << _day << endl;
	}

private:
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1(2024, 4, 28);
	d1.Print();

	Date d2(2024, 4, 27);
	d2.Print();

	return 0;
}

三：取地址及const取地址操作符重载

这两个默认成员函数一般不用重新定义，编译器默认会生成。

class Date
{
public:
	Date* operator&()
	{
		return this;
	}

	const Date* operator&()const
	{
		return this;
	}
private:
	int _year;
	int _month;
	int _day;
};

这两个运算符一般不需要重载，使用编译器生成的默认取地址的重载即可，只有特殊情况，才需
要重载，比如 想让别人获取到指定的内容！