1. 封装

1.1. struct

当单一变量无法完成描述需求的时候，结构体类型解决了这一问题。可以将多个类型打包成一体，形成新的类型，这是c语言中的封装
但是，新类型并不包含，对数据类的操作。所有操作都是通过函数的方式进行封装的
struct Date

// c语言的封装 数据放到  一起用struct打包，然后把数据以引用或指针的方式传给行为
// c++认为c语言封装不彻底
// 数据和行为分离，没有权限控制    对内数据开放，逻辑抽象，对外提供接口
struct Date
{int year;int month;int day;
};
void init(Date &d)
{cin >> d.year >> d.month >> d.day;
}
void print(Date &d)
{cout << d.year << " " << d.month << " " << d.day << endl;
}
bool isLeapYear(Date &d)
{if (d.year % 4 == 0 || d.year % 400 == 0 && d.year % 100 != 0)return true;elsereturn false;
}int main()
{Date d;init(d);print(d);if (isLeapYear(d))cout << d.year << " is leap year" << endl;elsecout << d.year << " is not leap year" << endl;return 0;
}

1.2. 封装

封装，可以实现对外提供接口，屏蔽数据，对内开放数据
比如：用struct封装的类，既知其接口，又可以直接访问其内部数据，这样却没有达到信息隐蔽的功效，而class则提供了这样的功能，屏蔽内部数据，对外开放接口
struct中所有行为和属性都是public的(默认)，c++中class可以指定行为和属性的访问方式，默认为private

1.3. 用class封装带行为的类

class封装的本质，在于将数据和行为，绑定在一起通过对象来完成操作
class Date

// 权限控制 private protected public
// 数据和行为在一起
// 对内开放数据，逻辑抽象，对外提供接口
// 类 类对象 对象，调用行为完成需求
class Date
{
public:void init(){cin >> year >> month >> day;}void print(){cout << "year:" << "month:" << "day" << endl;cout << year << month << day << endl;}bool isLeapYear(){if (year % 4 == 0 || year % 400 == 0 && year % 100 != 0)return true;elsereturn false;}int getYear(){return year;}protected:int year;private:int month;int day;
};
int main()
{Date d;// d.year = 3000; // privated.init();d.print();if (d.isLeapYear())cout << d.getYear() << " is leap year" << endl;elsecout << d.getYear() << " is not leap year" << endl;return 0;
}

Date类访问自己的成员，可以不需要通过传引用的方式

class Date
{
public:void init(); // 函数成员void print();bool isLeapYear();int getYear();protected:int year;private:int month; // 数据成员int day;
};
void Date::init()
{cin >> year >> month >> day;
}
void Date::print()
{cout << "year:" << "month:" << "day" << endl;cout << year << month << day << endl;
}
bool Date::isLeapYear()
{if (year % 4 == 0 || year % 400 == 0 && year % 100 != 0)return true;elsereturn false;
}
int Date::getYear()
{return year;
}
int main()
{Date d;// d.year = 3000; // privated.init();d.print();if (d.isLeapYear())cout << d.getYear() << " is leap year" << endl;elsecout << d.getYear() << " is not leap year" << endl;return 0;
}

date.h

#ifndef DATE_H
#define DATE_H// 类名其实也是一种变相的命名空间
namespace Space
{class Date{public:void init(); // 函数成员void print();bool isLeapYear();int getYear();protected:int year;private:int month; // 数据成员int day;};
}#endif

date.cpp

#include "date.h"
#include <iostream>using namespace std;
namespace Space
{void Date::init(){cin >> year >> month >> day;}void Date::print(){cout << "year:" << "month:" << "day" << endl;cout << year << month << day << endl;}bool Date::isLeapYear(){if (year % 4 == 0 || year % 400 == 0 && year % 100 != 0)return true;elsereturn false;}int Date::getYear(){return year;}
}

main.cpp

// 声明和实现要分开
#include "date.h"
using namespace Space;int main()
{Date d;// d.year = 3000; // privated.init();d.print();if (d.isLeapYear())cout << d.getYear() << " is leap year" << endl;elsecout << d.getYear() << " is not leap year" << endl;return 0;
}

2. 练习封装

2.1. 封装自己的list

main.cpp

class List
{
public:List *createList();void insertList(int d);void traverseList();private:struct Node{int data;struct Node *next;} *head;
};List *List::createList()
{head = new Node;head->next = NULL;return this;
}
void List::insertList(int d)
{Node *cur = new Node;cur->data = d;cur->next = head->next;head->next = cur;
}
void List::traverseList()
{Node *ph = head->next;while (ph != NULL){cout << ph->data << endl;ph = ph->next;}
}int main()
{List list;list.createList();for (int i = 0; i < 10; i++){list.insertList(i);}list.traverseList();return 0;
}