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C++篇类和对象（3）万能工具怎么用？

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在这里插入图片描述
重难点：

这里重载为全局的面临对象访问私有成员变量的问题：

有4种解决方法：

1.成员放在公有（也就是把private注释掉）；
2.Date提供getxxx函数；
3.友元函数；（随后介绍）；
4.重载为成员函数。下面有图示：

在这里插入图片描述
2.重载为成员函数

#include<iostream>
using namespace std;
class Date
{
public:Date(int year = 1, int month = 1, int day = 1){_year = year;_month = month;_day = day;}void Print(){cout << _year << "/" << _month << "/" << _day << endl;}
//private://1.成员放在公有位置，注释掉privateint _year;int _month;int _day;};
//重载为全局的面临对象访问私有成员变量的问题
bool operator==(const Date& d1, const Date& d2)
{return d1._year == d2._year&& d1._month == d2._month&& d1._day == d2._day;}
int main()
{Date d1(2025, 9, 18);Date d2(2025, 9, 20);d1.Print();d2.Print();return 0;
}

#include<iostream>
using namespace std;
class Date
{public:Date(int year = 1, int month = 1, int day = 1){_year = year;_month = month;_day = day;}void Print(){cout << _year << "/" << _month << "/" << _day << endl;}bool operator==(const Date& d){return _year == d._year&& _month == d._month&& _day == d._day;}
private:int _year;int _month;int _day;};
//重载为全局的面临对象访问私有成员变量的问题：重载为成员函数
//bool operator==(const Date& d)
//{
//	return _year == d._year
//		&& _month == d._month
//		&& _day == d._day;
//
//}
int main()
{Date d1(2025, 9, 18);Date d2(2025, 9, 20);d1.operator==(d2);//运算符重载函数可以显示调用d1 == d2;//编译器会转换成d1.operator==(d2);return 0;
}

日期类实现更好理解赋值运算符重载，运算符重载

日期加加
日期减减

//Date.cpp

#include"Date.h"
//声明和定义分离
void Date::Print()const
{cout << _year << "/" << _month << "/" << _day << endl;
}bool Date::CheckDate()
{if (_month > 12 || _month < 0 || _day<0 || _day> GetMonthDay(_year, _month)){return false;}else{return true;}
}Date::Date(int year, int month, int day)
{_year = year;_month = month;_day = day;if (!CheckDate()){cout << "日期非法" << endl;}
}
//方法1：引用返回
Date& Date::operator+=(int day)//为了不改变原来的d1，所以这里用引用
{_day += day;//先把天数加上去while (_day > GetMonthDay(_year, _month))//如果超过当前月份的天数，就结束{_day -= GetMonthDay(_year, _month);++_month;if (_month == 13){++_year;_month = 1;}}return *this;
}
//方法2：拷贝传值
Date Date::operator+(int day)
{Date tmp = *this;//tmp拷贝一份d1，这里不改变d1的值tmp._day += day;//先把天数加上去while (tmp._day > GetMonthDay(tmp._year, tmp._month))//如果超过当前月份的天数，就结束{tmp._day -= GetMonthDay(tmp._year, tmp._month);++tmp._month;if (tmp._month == 13){tmp._month = 1;tmp. _year++;}}return tmp;//返回tmp，局部对象
}//
Date& Date::operator-=(int day)
{_day -= day;while (_day <= 0)//要进去循环一定是天数成了负数{--_month;if (_month == 0){_month = 12;--_year;}_day += GetMonthDay(_year, _month);}return *this;
}Date Date::operator-(int day)
{Date tmp = *this;tmp._day -= day;while (tmp._day <= 0){--tmp._month;if (tmp._month == 0){tmp._month == 12;--tmp._year;}tmp._day += GetMonthDay(tmp._year, tmp._month);}return tmp;
}

//Date.h

#pragma once
#include<iostream>
#include<assert.h>using namespace std;
class Date
{public:Date(int year = 1900, int month = 1, int day = 1);void Print()const;int GetMonthDay(int year, int month){assert(month > 0 && month < 13);//函数需要频繁调用，应该放到静态区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;}else{return MonthDayArray[month];}}bool CheckDate();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);Date operator-(int day);Date& operator-=(int day);private:int _year;int _month;int _day;
};

//test.cpp

int main()
{Date d1(2025, 9, 23);Date d2 = d1 + 100;Date d4 = d1 - 100;d1.Print();//2025,9,23d2.Print();//2026,1,1d4.Print();//2025,6,15return 0;
}

日期加减

//Date.cpp

//d1++
//d1.operator(0)后置++有拷贝
Date Date::operator++(int)
{Date tmp (*this);//先保存当前对象的原始值*this += 1;//对当前对象进行自增return tmp;//返回原始值的拷贝
}//++d1
//d1.operator()前置++没有拷贝
Date& Date::operator++()
{*this += 1;//先对当前对象进行自增return *this;//返回自增之后的对象引用
}//d1--
//d1.operator(0)后置--有拷贝
Date Date::operator--(int)
{Date tmp(*this);//先保存当前对象的原始值*this -= 1;//对当前对象进行自增return tmp;//返回原始值的拷贝
}//--d1
//d1.operator()前置--没有拷贝
Date& Date::operator--()
{*this -= 1;//先对当前对象进行自增return *this;//返回自增之后的对象引用
}

//Date.h

Date& operator++();
Date operator++(int);
Date& operator--();
Date operator--(int);

//Test测试

#include"Date.h"void TestDate01()
{Date d1(2025, 9, 23);Date ret1 = d1++;ret1.Print();//2025 9 23  后置++返回值是++之前的值d1.Print();//2025 9 24Date d2(2025, 9, 23);Date ret2 = ++d2;ret2.Print();//2025 9 24  前置返回值++自己也要++d2.Print();//2025 9 24Date d3(2025, 9, 23);Date ret3 = d3--;ret3.Print();//2025 9 23  d3.Print();//2025 9 22Date d4(2025, 9, 23);Date ret4 = --d4;ret4.Print();//2025 9 22 d4.Print();//2025 9 22
}int main()
{TestDate01();return 0;
}

日期相减

//Date.cpp

//d1-d2
int Date::operator-(const Date& d)const
{int flag = 1;Date max = *this;Date min = d;if (*this < d)//假设认为d1大于d2,这里是假设错了走if循环进行判断{max = d;min = *this;flag = -1;//如果d1小，d2大，flag为负数，算出来的差值天数为负数，这里解决这个问题}int n = 0;while (min != max){++min;++n;}return n * flag;
}

//Date.h

int operator-(const Date& d)const;

//Test2测试

#include"Date.h"void TestDate2()
{Date d5(2025, 9, 23);Date d6(2025, 5, 21);cout << d5 - d6 << endl;//125
}
int main()
{TestDate2();return 0;
}

流插入流提取算日期相差的天数：（在终端自己输入）

//Date.cpp

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)
{while (1){cout << "请依次输入年月日：>";in >> d._year >> d._month >> d._day;if (!d.CheckDate()){cout << "输入日期非法";d.Print();cout << "请重新输入：>" << endl;}else{break;}}return in;
}

//Date.h

#pragma once
#include<iostream>
#include<assert.h>using namespace std;
class Date
{//友元函数，可以访问私有成员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;int GetMonthDay(int year, int month){assert(month > 0 && month < 13);//函数需要频繁调用，应该放到静态区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;}else{return MonthDayArray[month];}}bool CheckDate();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);Date operator-(int day);Date& operator-=(int day);Date& operator++();Date operator++(int);Date& operator--();Date operator--(int);int operator-(const Date& d)const;//void operator<<(ostream& out);
//private:int _year;int _month;int _day;
};
ostream& operator<<(ostream& out, const Date& d);
istream& operator>>(istream& in, Date& d);

//test测试：

#include"Date.h"void TestDate3()
{Date d1, d2;//d1 << cout;//这样写不好看，调整不了参数，所以建议写成全局的//d1.operator<<(cout);cin >> d1 >> d2;cout << d1 << d2;operator<<(cout, d1);cout << d1 - d2 << endl;
}
int main()
{TestDate3();return 0;
}