日期类的实现

class Date
{
public:
	// 获取某年某月的天数
	int GetMonthDay(int year, int month) {
		static int days[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };
		int day = days[month];
		if ((month == 2) && ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)))
			day++;
		return day;
	}

	// 全缺省的构造函数
	Date(int year = 1900, int month = 1, int day = 1) {
		if (year < 1900 || month < 1 || month >12 || day < 1 || day>GetMonthDay(year, month)) {
			cout << "wrong date" << endl;
		}
		_year = year;
		_month = month;
		_day = day;
	}
	// 拷贝构造函数
  // d2(d1)
	Date(const Date& d) {
		this->_year = d._year;
		this->_month = d._month;
		this->_day = d._day;
	}
	// 赋值运算符重载
  // d2 = d3 -> d2.operator=(&d2, d3)
	Date& operator=(const Date& d) {
		if (this != &d) {
			_year = d._year;
			_month = d._month;
			_day = d._day;
		}
		return *this;
	}
	// 析构函数
	~Date() {
		_year = 0;
		_month = 0;
		_day = 0;
	}
	void displsy() {
		cout << _year << " " << _month << " " << _day << endl;
	}
	// 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 > 12) {
				_month -= 12;
				_year++;
			}
		}
		return *this;
	}
	// 日期+天数
	Date operator+(int day) {
		return *this += day;
	}
	// 日期-天数
	Date operator-(int day) {
		return *this -= day;
	}
	// 日期-=天数
	Date& operator-=(int day) {
		if (day < 0) {
			return *this += -day;
		}
		while (_day <= day) {
			_month--;
			if (_month == 0) {
				_month = 12;
				_year--;
			}
			_day += GetMonthDay(_year, _month);
		}
		_day -= day;
		return *this;
	}
	// 前置++
	Date& operator++() {
		return *this += 1;
	}
	// 后置++
	Date operator++(int) {
		Date d = *this;
		*this += 1;
		return d;
	}
	// 后置--
	Date operator--(int) {
		Date d = *this;
		*this -= 1;
		return d;
	}
	// 前置--
	Date& operator--() {
		return *this -= 1;
	}
	// >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 _year == d._year
			&& _month == d._month
			&& _day == d._day;
	}
	// >=运算符重载
	inline bool operator >= (const Date& d) {
		return *this > d || *this == d;
	}
	// <运算符重载
	bool operator < (const Date& d) {
		return !(*this >= d);
	}
	// <=运算符重载
	bool operator <= (const Date& d) {
		return !(*this > d);
	}
	// !=运算符重载
	bool operator != (const Date& d) {		
		return !(*this == d);
	}
	//日期-日期 返回天数
	int operator-(const Date& d) {
		Date min = d;
		Date max = *this;
		int flag = 1;
		if (*this < d) {
			flag = -1;
			max = d;
			min = *this;
		}
		int day = 0;
		while (min < max) {
			max--;
			day++;
		}
		return day * flag;
	}
private:
	int _year;
	int _month;
	int _day;

};