C++初阶小项目——日期类的实现

前言：在完成c++入门基础及类和对象初步了解，旨在通过此项目完成类和对象相关操作的实践

一，完成准备工作

与之前类似，建立Date.h Date.cpp Test.cpp三个文件

Date.h

完成类及类函数的声明

Date.cpp

完成具体函数的实现

Test.cpp

测试程序可执行性

二， 具体函数的实现

1，构造函数Date(int year = 1900, int month = 1, int day = 1); 

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

可以检查日期准确性 

if (!CheckDate())
{cout << "⽇期⾮法" << endl;
}

总代码 

Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckDate()){cout << "⽇期⾮法" << endl;}}

2，void Print(); 

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

3，GetMonthDay(int year, int month)； 

//默认为内联函数incline
//频繁调用的简短内敛函数不用建立栈帧
int GetMonthDay(int year, int month)
{static int monthDayArray[13] = { -1, 31, 28, 31, 30, 31, 30 ,31, 31, 30, 31, 30, 31 };//判断闰年//能被4整除，但不能被100整除//能被400整除if (month == 2 && (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)){return 29;}return monthDayArray[month];
}

assert(month > 0 && month < 13);

int GetMonthDay(int year, int month)
{assert(month > 0 && month < 13);static int monthDayArray[13] = { -1, 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;}return monthDayArray[month];
}

注：该函数建立在类里面，因为类里面默认为内联函数incline，频繁调用的简短内敛函数不用建立栈帧 

 month == 2 在 (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)

因为这样减少判断，极高效率

4，Date& operator+=(int day);  

思路：先加上天数与当月总天数比较，比总天数大则减去 当月总天数 月份加一

单独考虑12月变为1月

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

//第一种
Date d2 = d1 + 100;
//第二种
Date d3(d1 + 100);

注：需考虑day为负数 

if (day < 0)
{return *this -= (-day);
}

总代码 

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 == 13){_year++;_month = 1;}}return *this;
}

5，Date operator+(int day) ; 

第一种

Date Date::operator+(int day)
{Date tmp = *this;tmp._day += day;while (tmp._day > GetMonthDay(tmp._year, tmp._month)){tmp._day -= GetMonthDay(tmp._year, tmp._month);++tmp._month;if (tmp._month == 13){tmp._year++;tmp._month = 1;}}return tmp;
}

d1 += 100;
d1.Print();

第二种（复用）

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

注：4和5注意引用的使用 

6，Date& operator-=(int day);

思路：先减天数，如果差<0 则月减一（一月变十二月单独考虑 年也要减一）差加上此时月总天数

第一种 

Date& Date::operator-=(int day)
{_day -= day;while (_day <= 0){--_month;if (_month == 1){_month = 12;--_year;}_day += GetMonthDay(_year, _month);}return *this;
}

第二种（复用） 

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

 注：需考虑day为负数 

if (day < 0)
{return *this += (-day);
}

总代码 

Date& Date::operator-=(int day)
{if (day < 0){return *this += (-day);}_day -= day;while (_day <= 0){--_month;if (_month == 1){_month = 12;--_year;}_day += GetMonthDay(_year, _month);}return *this;
}

7，Date operator-(int day);   

第一种（复用） 

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

第二种 

Date Date::operator-(int day)
{Date tmp = *this;tmp._day -= day;while (tmp._day <= 0){--tmp._month;if (tmp._month == 1){tmp._month = 12;--tmp._year;}tmp._day += GetMonthDay(tmp._year, tmp._month);}return tmp;
}

思考： -复用-=   和   -=复用-   哪个好

结论：-复用-= 更优

原因：

实现 - tmp都需要两次拷贝，效果一样的

-=复用- 也需要拷贝（多了三次拷贝）

8，bool operator<(const Date& d); 

bool Date::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){return _day < d._day;}return false;
}

9，bool operator==(const Date& d); 

bool Date::operator==(const Date& d)
{return _year == d._year&& _month == d._month&& _day == d._day;
}

利用8和9 可以完成其他比较函数 

10，bool operator<=(const Date& d); 

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

11，bool operator>(const Date& d); 

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

12，bool operator>=(const Date& d); 

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

13，bool operator!=(const Date& d); 

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

14， Date& operator++();

前置 

重载++运算符时，有前置++和后置++，运算符重载函数名都是operator++，⽆法很好的区分。C++规定，后置++重载时，增加⼀个int形参，跟前置++构成函数重载，⽅便区分。

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

15，Date operator++(int); 

后置 （比前置多了拷贝，更推荐前置++）

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

16,Date& operator--();

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

17,Date operator--(int); 

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

 18，int operator-(const Date& d);

日期-日期=天数

方法论：判断大小，小循环+1到与大相同，此时加的次数即为天数 

int Date::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;
}

19，bool CheckDate(); 

bool Date::CheckDate()
{if (_month < 1 || _month > 12|| _day < 1 || _day > GetMonthDay(_year, _month)){return false;} else{return true;}
}

20，ostream& operator<<(ostream& out, const Date& d); 

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

21，istream& operator>>(istream& in, Date& d);

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

重载<<和>>时，需要重载为全局函数，因为重载为成员函数，this指针默认抢占了第⼀个形参位置，第⼀个形参位置是左侧运算对象，调⽤时就变成了 对象<<cout，不符合使⽤习惯和可读性。重载为全局函数把ostream/istream放到第⼀个形参位置就可以了，第⼆个形参位置当类类型对象。 

20,21为全局函数

可以用 友元函数声明 来访问类的数据 

需要连续输出，流插入为从左向右，故返回值应为 out

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

22，变为const成员函数 

 在不改变对象的前提下，建议写成const成员函数

三，总代码预览 

 Date.h

#pragma once
#include<iostream>
using namespace std;
#include<assert.h>class Date
{// 友元函数声明friend ostream& operator<<(ostream& out, const Date& d);friend istream& operator>>(istream& in, Date& d);public:Date(int year = 1900, int month = 1, int day = 1);void Print() const;//默认为内联函数incline//频繁调用的简短内敛函数不用建立栈帧int GetMonthDay(int year, int month) const{assert(month > 0 && month < 13);static int monthDayArray[13] = { -1, 31, 28, 31, 30, 31, 30 ,31, 31, 30, 31, 30, 31 };//判断闰年//能被4整除，但不能被100整除//能被400整除if (month == 2 && (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)){return 29;}return monthDayArray[month];}bool CheckDate() 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;bool operator!=(const Date& d) const;// d1 += 天数Date& operator+=(int day);Date operator+(int day) const;// d1 -= 天数Date& operator-=(int day);Date operator-(int day)const;Date& operator++();Date operator++(int);Date& operator--();Date operator--(int);int operator-(const Date& d) const;private:int _year;int _month;int _day;
};// 重载
ostream& operator<<(ostream& out, const Date& d);
istream& operator>>(istream& in, Date& d);

Date.cpp 

#include"Date.h"Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckDate()){cout << "⽇期⾮法" << endl;}}void Date::Print() const
{cout << _year << "-" << _month << "-" << _day << endl;
}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 == 13){_year++;_month = 1;}}return *this;
}Date Date::operator+(int day) const
{Date tmp = *this;tmp += day;/*tmp._day += day;while (tmp._day > GetMonthDay(tmp._year, tmp._month)){tmp._day -= GetMonthDay(tmp._year, tmp._month);++tmp._month;if (tmp._month == 13){tmp._year++;tmp._month = 1;}}*/return tmp;
}Date& Date::operator-=(int day)
{if (day < 0){return *this += (-day);}_day -= day;while (_day <= 0){--_month;if (_month == 1){_month = 12;--_year;}_day += GetMonthDay(_year, _month);}return *this;
}
//第二种
//Date& Date::operator-=(int day)
//{
//	*this = *this - day;
//	return *this;
//}Date Date::operator-(int day) const
{Date tmp = *this;tmp -= day;//tmp._day -= day;//while (tmp._day <= 0)//{//	--tmp._month;//	if (tmp._month == 1)//	{//		tmp._month = 12;//		--tmp._year;//	}//	tmp._day += GetMonthDay(tmp._year, tmp._month);//}//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;
}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);
}bool Date::operator!=(const Date& d) const
{return !(*this == d);
}Date& Date::operator++()
{*this += 1;return *this;
}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) const
{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;
}bool Date::CheckDate() const
{if (_month < 1 || _month > 12|| _day < 1 || _day > GetMonthDay(_year, _month)){return false;} else{return true;}
}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)
{cout << "请依次输⼊年⽉⽇:>";in >> d._year >> d._month >> d._day;if (!d.CheckDate()){cout << "⽇期⾮法" << endl;}return in;
}