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前言

C++日期类的完整实现，以及this指针的const修饰等的介绍

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一、日期类的实现

// Date.h
#pragma once

#include <iostream>
using namespace std;

#include <assert.h>

class Date
{
	// 友元函数
	friend ostream& operator<<(ostream& out, const Date& d);
	friend istream& operator>>(istream& in, Date& d);
public:
	// 构造函数
	Date(int year = 1970, int month = 1, int day = 1);

	void Print() const
	{
		cout << _year << '-' << _month << '-' << _day << endl;
	}

	// 拷贝构造函数
	Date(const Date& d);

	// 析构函数
	~Date();

	// 赋值运算符重载
	Date& operator=(const Date& d);

	// 运算符重载
	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;

	// 获取每月天数
	int GetMonthDay(int year, int month);

	// + += - -= 天数
	Date& operator+=(const int day);
	Date operator+(const int day) const;
	Date& operator-=(const int day);
	Date operator-(const int day) const;

	// 前置++
	Date& operator++();

	// 后置++
	Date operator++(int);

	// 前置--
	Date& operator--();

	// 后置--
	Date operator--(int);

	// 日期-日期
	int operator-(const Date& d) const;

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



// 流插入
ostream& operator<<(ostream& out, const Date& d);

// 流提取
istream& operator>>(istream& in, Date& d);

---

// Date.cpp
#define  _CRT_SECURE_NO_WARNINGS

#include "Date.h"

// 构造函数
Date::Date(int year, int month, int day)
{
	if (month > 0 && month < 13 && day > 0 && day <= GetMonthDay(year, month))
	{
		_year = year;
		_month = month;
		_day = day;
	}
	else
	{
		cout << "非法日期" << endl;
		assert(false);
	}

}

// 拷贝构造函数
Date::Date(const Date& d)
{
	_year = d._year;
	_month = d._month;
	_day = d._day;
}


// 析构函数
Date::~Date()
{
	_year = 0;
	_month = 0;
	_day = 0;
}


// 赋值运算符重载
Date& Date::operator=(const Date& d)
{
	if (this != &d)
	{
		_year = d._year;
		_month = d._month;
		_day = d._day;
	}

	return *this;
}

// 运算符重载
bool Date::operator<(const Date& d) const
{
	if (_year < d._year)
	{
		return true;
	}
	else if (_year == d._year && _month < d._month)
	{
		return true;
	}
	else if (_year == d._year && _month == d._month && _day == d._day)
	{
		return true;
	}
	else
	{
		return false;
	}
}

bool Date::operator==(const Date& d) const
{
	if (_year != d._year)
	{
		return false;
	}
	else if (_year == d._year && _month != d._month)
	{
		return false;
	}
	else if (_year == d._year && _month == d._month && _day != d._day)
	{
		return false;
	}
	else
	{
		return true;
	}
}


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);
}

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


// 获取月份天数
int Date::GetMonthDay(int year, int month)
{
	static int dayArray[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;
	}
	else
	{
		return dayArray[month];
	}
}

// + += - -= 天数
Date& Date::operator+=(const int day)
{
	if (_day < 0)
	{
		return *this -= -_day;
	}
	_day += day;
	while (_day > GetMonthDay(_year, _month))
	{
		_day -= GetMonthDay(_year, _month);
		_month++;
		if (_month == 13)
		{
			_year++;
			_month = 1;
		}
	}

	return *this;
}


Date Date::operator+(const int day) const
{
	Date tmp(*this);

	tmp += day;

	return tmp;
}


Date& Date::operator-=(const int day)
{
	if (_day < 0)
	{
		return *this += -_day;
	}
	_day -= day;
	while (_day <= 0)
	{
		_month--;
		if (_month == 0)
		{
			_year--;
			_month = 12;
		}
		_day += GetMonthDay(_year, _month);
	}

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

	tmp -= day;

	return tmp;
}


// 前置++
Date& Date::operator++()
{
	*this += 1;

	return *this;
}

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

// 前置--
Date& Date::operator--()
{
	*this -= 1;
	return *this;
}

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


// 日期-日期
int Date::operator-(const Date& d) const
{
	Date max = *this;
	Date min = d;
	int flag = 1;

	if (max < min)
	{
		max = d;
		min = *this;
		flag = -1;
	}
	int num = 0;
	while (min != max)
	{
		num++;
		++min;
	}

	return num * flag;
}


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

	return out;
}

istream& operator>>(istream& in, Date& d)
{
	int year, month, day;
	in >> year >> month >> day;
	if (month > 0 && month < 13 && day > 0 && day <= d.GetMonthDay(year, month))
	{
		d._year = year;
		d._month = month;
		d._day = day;
	}
	else
	{
		cout << "非法日期" << endl;
		assert(false);
	}


	return in;
}

---

// test.cpp
#define  _CRT_SECURE_NO_WARNINGS

#include "Date.h"

void TestDate1()
{
	Date d1(2023, 9, 1);
	Date d2(2000, 1, 1);
	Date d3(2000, 3, 1);

	cout << (d1 < d2) << endl;
	cout << (d1 == d2) << endl;
	cout << (d2 == d3) << endl;
	cout << (d1 <= d2) << endl;
	cout << (d1 > d2) << endl;
	cout << (d2 <= d3) << endl;
	cout << (d2 > d3) << endl;

	Date d4(1949, 10, 1);
	Date d5(1949, 10, 1);
	cout << (d4 != d5) << endl;
}

void TestDate2()
{
	Date d1(2024, 5, 5);

	d1 += 1000;
	d1.Print();

	Date d2(2024, 10, 1);
	(d2 + 100).Print();

	Date d3(2024, 12, 31);
	d3 -= 100;
	d3.Print();
}


void TestDate3()
{
	Date d1(2024, 5, 5);
	Date d2(2050, 12, 30);

	cout << d1 - d2 << endl;
	cout << d2 - d1 << endl;
}

void TestDate4()
{
	Date d1(2024, 5, 5);
	Date d2(2050, 12, 30);
	Date d3(1328, 1, 4);

	d1 = d2 = d3;
}


void TestDate5()
{
	Date d1(2024, 5, 5);
	Date d2(2050, 12, 30);
	Date d3(1328, 1, 4);

	d1 += 1000;

	d2 -= 50;

	d3 += 500;

	cout << d1;
	cout << d2;
	cout << d3;
}

void TestDate6()
{
	Date d1;
	Date d2;

	cin >> d2 >> d1;
	cout << d1 << d2;

}


void TestDate7()
{
	Date d1(1328, 1, 1);
	d1.Print();


	const Date d2(1368, 1, 4);
	d2.Print();

}


void TestDate8()
{
	Date d1(1328, 1, 1);

	const Date d2(1368, 1, 4);

	cout << (d1 < d2) << endl;

}

int main()
{
	TestDate8();
	
	return 0;
}

二、this指针的const修饰

// 简单的日期类
#include <iostream>
using namespace std;

class Date
{
public:
	Date(int year = 1368, int month = 1, int day = 4)
	{
		_year = year;
		_month = month;
		_day = day;
	}

	void Print() 
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}

	Date(const Date& d)
	{
		_year = d._year;
		_month = d._month;
		_day = d._day;
	}

	~Date()
	{
		_year = 0;
		_month = 0;
		_day = 0;
	}
private:
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1(1949, 10, 1);
	d1.Print();

	const Date d2(1945, 8, 15);
	d2.Print();
	

	return 0;
}

上述日期类实现无法打印d2，原因如下：
使用const修饰创建类，使d2在调用Print函数时，传入的this指针是有const修饰的，与日期类定义类型冲突，所以报错。如下：

修改如下：

	void Print() const
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}

使this指针变为const修饰，需要在成员函数名后加const修饰。

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总结

C++日期类的完整实现，以及this指针的const修饰等的介绍