【落羽的落羽 C++】日期类（Date）的完整实现

class Date
{
public:

	// 获取某年某月的天数
    int GetMonthDay(int year, int month)
	{
		static int monthDayArray[13] = { -1,31,28,31,30,31,30,31,31,30,31,30,31 };
		//特殊情况是闰年的二月
		if (month == 2 && ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)))
		{
			return 29;
		}
		else
		{
			return monthDayArray[month];
		}
	}


	// 全缺省的构造函数
	Date(int year = 1900, int month = 1, int day = 1)
		:_year(year)
		, _month(month)
		, _day(day)
	{
	}


	// 拷贝构造函数
    // d2(d1)
	Date(const Date& d)
		:_year(d._year)
		, _month(d._month)
		, _day(d._day)
	{
	}


	// 赋值运算符重载
    // d2 = d3 -> d2.operator=(&d2, d3)
	Date& operator=(const Date& d)
	{
		_year = d._year;
		_month = d._month;
		_day = d._day;
		return *this;
	}


	// 析构函数
	~Date()
	{
	}

    // 友元声明
	friend ostream& operator<<(ostream& out, const Date& d);
	friend istream& operator>>(istream& out, Date& d);

	// 日期+=天数
	Date& operator+=(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;
	}

	// 日期+天数
	Date operator+(int day)
	{
		Date ret = *this;
		ret += day;
		return ret;
	}


	// 日期-天数
	Date operator-(int day)
	{
		Date ret = *this;
		ret -= day;
		return ret;
	}

	// 日期-=天数
	Date& operator-=(int day)
	{
		if (day < 0)
		{
			return *this += -day;
		}

		_day -= day;
		while (_day <= 0)
		{
			--_month;
			if (_month == 0)
			{
				_month = 12;
				--_year;
			}
			_day += GetMonthDay(_year, _month);
		}
		return *this;
	}


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


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


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

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


	// >运算符重载
	bool operator>(const Date& d)
	{
		return !(*this <= d);
	}


	// ==运算符重载
	bool operator==(const Date& d)
	{
		return _year == d._year
			&& _month == d._month
			&& _day == d._day;
	}


	// >=运算符重载
	bool operator>=(const Date& d)
	{
		return !(*this < d);
	}

	// <运算符重载
	bool 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 operator <= (const Date& d)
	{
		return *this == d || *this < d;
	}


	// !=运算符重载
	bool operator != (const Date& d)
	{
		return !(*this == d);
	}

	// 日期-日期，返回相差的天数
	int operator-(const Date& d)
	{
		Date max = *this;
		Date min = d;
		int flag = 1;
		if (*this < d)
		{
			max = d;
			min = *this;
			flag = -1;
		}
		int n = 0;
		while (min != max)
		{
			++min;
			++n;
		}
		return n * flag;
	}

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

ostream& operator<<(ostream& out, const Date& d)
{
	out << d._year << ' ' << d._month << ' ' << d._day;
	return out;
}

istream& operator>>(istream& in, Date& d)
{
	cout << "请依次输入年月日：" << endl;
	in >> d._year >> d._month >> d._day;
	if (d._month < 1 || d._month>12 || d._day<1 || d._day>d.GetMonthDay(d._year, d._month))
	{
		cout << "日期非法" << endl;
	}
	return in;
}