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;
}