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;
}