c-＞c++(二):class

        本文主要探讨C++类的相关知识。

构造和析构函数
        构造函数(可多个)：对象产生时调用初始化class属性、分配class内部需要的动态内存
        析构函数（一个）：对对象消亡时调用回收分配动态内存
        C++提供默认构造和析构,构造函数可重载,析构函数不需重载
        构造和析构函数不需要返回值类型,构造函数可带参或不带参,析构函数不带参
        无其他构造函数时默认构造函数可省略,有构造函数时默认构造函数不能省
        class声明时可给构造函数形参赋默认值,调用时不传参则使用默认值,调用不能有重载歧义
        所有参数都带默认值构造函数,可以表示所有构造函数
        拷贝构造函数：用对象来初始化对象,函数不需重载
        浅拷贝:普通成员变量初始化的拷贝构造函数(默认提供),有动态内存分配时出错
        深拷贝:浅拷贝无法拷贝对象的成员指针已分配的内存空间,深拷贝可以
        拷贝显式提供copy constructor为深拷贝,拷贝构造函数用原来的析构函数

权限
        public类内、类外可访问,子类可访问父类公共成员
        protected类内可访问,类外不可,子类可访问父类保护成员
        private类内可访问,类外不可,子类不可访问父类私有成员
        默认是private继承,struct是public继承
        继承中父类所有权限继承给子类
        public继承：父类成员在子类中保持原有访问权限
        private继承：父类成员在子类中变为private权限
        protected继承：父类public变protected,protected为protected,private为private
        using：private/protected继承父类public中成员后权限变小,可通过using回归到public权限

struct和class
        C不支持成员函数,C++支持
        C不支持static成员,C++中支持
        C默认public,C++默认public,c++可指定public/private/protected权限
        C不支持继承(通过包含结构体指针实现),C++支持且struct和class可互相继承
        C++中struct和class:struct默认public,class默认private,struct和class交叉继承权限取决子类

派生类和基类
        派生类不继承基类构造和析构函数,只继承成员变量和成员方法,派生类有自己构造和析构
        派生类构造函数执行前,先调用基类构造函数,再调用自己构造函数
        派生类先执行自己析构函数,再执行基类析构函数
        派生类覆盖基类同名成员(重定义),父类的同名成员存在且被隐藏,可通过全域路径调用被隐藏的方法,可添加派生类独有成员
        派生类是基类的超集,基类对象放大成派生类可能出错,派生类赋值给基类可正常使用(类似char和int的兼容性)

多继承二义性和多态
        C多继承A和B,A和B有同名成员、菱形继承(B1:A, B2:A, C:B1,B2)造成二义性
        全域路径调用方法,重定义子类方法,重写虚函数解决二义性
        基类方法声明为virtual,派生类重写同名方以实现多态
        重载函数名相同参数列表不同,重定义子类实现父类同名方法后把父类方法隐藏
        重写子类去实现父类同名virtual方法实现多态特性

虚函数
        抽象类:有纯虚函数的类,抽象类只能为基类派生新类,不可实例化对象
        派生类必须实现基类纯虚函数才能用于实例化对象,否则派生类仍为基类
        接口：类中所有成员函数是public且是纯虚函数

        无虚构造函数,包含虚函数的类只能作为基类派生新类,无法实例化对象,构造函数是在实例化的时候被调用的,故无虚构造函数
        抽象基类(接口)指针指向派生类(new派生类对象：person *p = new man; delete p;),抽象基类(接口)析构函数需要为虚,才可删除指针时能正确调用派生类析构函数,否则不会调用派生类析构函数
        抽象基类(接口)指针指向派生类(定义好的派生类man m;person *p = &m;),抽象基类(接口)析构函数是否为虚,都能正常调用派生类析构函数,一般抽象基类(接口)的析构函数都定义为虚

运算符重载
        运算符重载是重定义对象运算符对应函数
        赋值运算符=默认提供,重载有指针成员时涉及浅拷贝和深拷贝
        ++a对应Type& operator++(void);

        a++,对应Type& operator++(int x);
        不可重载运算符:   .,.*, ->*,sizeof,?,:,#

静态成员
        静态成员属于class本身,不属于对象
        静态成员变量在类的多个对象中均可访问,且是同一个
        静态成员变量和方法可以用对象调用,也可不产生对象的本身调用
        静态数据成员不在类中初始化,类只定义模版
        静态数据成员不在类构造函数中初始化,构造函数用于构建对象时初始化对象成员
        静态数据成员值默认0,遵循public，private，protected访问准则
        静态方法只访问静态成员变量和方法,不能直接访问非静态,需要通过函数传参访问非静态
        静态成员变量可用于统计对象数
        静态类:内部全是静态成员,不能被实例化,不包括构造函数,不能实现接口(不能被继承),不能有实例成员
        静态类成员不能有protected或protected internal访问保护修饰符

友元函数
        友元函数不是本类成员函数,是外部函数
        友元函数在private或protected或public都可
        可以通过类来访问友元函数,不能直接通过友元函数访问类(常用传参访问)
        友元函数破坏了封装机制,实现类之间数据共享时减少系统开销,提高效率
        运算符重载可用友元函数除=,->,[],()
        类间的数据共享可用友元函数

demo1：

        类成员权限，构造和析构函数，深拷贝和浅拷贝

目录：

run.sh

#!/bin/bashif [ -f ./Makefile ]
thenmake clean
ficmake .makeecho "---------------------------------"./pro

CMakeLists.txt 

CMAKE_MINIMUM_REQUIRED(VERSION 2.20)                            #最低版本要求SET(CMAKE_CXX_COMPILER "g++")                                   #设置g++编译器PROJECT(CLASS)                                                  #设置工程名MESSAGE(STATUS "class test")                                    #打印消息ADD_EXECUTABLE(pro main.cpp person.cpp)                         #生成可执行文件

person.hpp

#ifndef __PERSON_HPP__
#define __PERSON_HPP__#include <iostream>using namespace std;namespace People
{class Person{public:string name;int age;string sex;string description;int *luck_num;Person();Person(string name = "xxx",int age = 0,string sex = "none",string description = "none");Person(const Person &p);~Person();void set_info(string name,int age,string sex,string description);void print_info();void set_income(int income);int  get_income();void set_savings_account(int savings_account);int  get_savings_account();private:int income;int savings_account;};}#endif

person.cpp

#include "person.hpp"
#include <iostream>using namespace std;void People::Person::set_info(string name,int age,string sex,string description)
{this->name = name;this->age = age;this->sex = sex;this->description = description; 
}void People::Person::print_info()
{cout << "name :" << this->name << endl;cout << "age :" << this->age << endl;cout << "sex :" << this->sex << endl;cout << "description :" << this->description << endl;cout << "income " << get_income() << endl;cout << "savings_account " << get_savings_account() << endl;cout << "luck_num : " << this->luck_num[0]  << " " << this->luck_num[1] << endl;
}void People::Person::set_income(int income)
{this->income = income;
}int  People::Person::get_income()
{return this->income;
}void People::Person::set_savings_account(int savings_account)
{this->savings_account = savings_account;
}int People::Person::get_savings_account()
{return this->savings_account;
}People::Person::Person()
{cout << "default constructor function" << endl;
}People::Person::Person(string name,int age,string sex,string description):name(name),age(age),sex(sex),description(description)
{this->luck_num = new int[2];cout << "user define constructor function" << endl;
}People::Person::~Person()
{delete [] this->luck_num;cout << "user define destructor function" << endl;
}
People::Person::Person(const Person &p):name(p.name),age(p.age),sex(p.sex),description(p.description)
{luck_num = new int(*p.luck_num);cout << "user define deep copy constructor function" << endl;
}

main.cpp 

#include <iostream>
#include "person.hpp"using namespace std;
using namespace People;int main()
{Person p1("xiaoming",23,"male","high");p1.set_income(50);p1.set_savings_account(100);p1.luck_num[0] = 2;p1.luck_num[1] = 7;p1.print_info();Person p2(p1);p2.set_income(20);p2.set_savings_account(10);p2.luck_num[0] = 36;p2.luck_num[1] = 72;p2.print_info();Person p3 = p2;p3.set_income(10);p3.set_savings_account(40);p3.luck_num[0] = 5;p3.luck_num[1] = 8;p3.print_info();return 0;
}

 结果示例：

demo2：

        继承和多态,虚函数，抽象类，接口

目录：

run.sh

#!/bin/bashif [ -f ./Makefile ]
thenmake clean
ficmake .makeecho "---------------------------------"./pro

 check_mem.sh

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --trace-children=yes -s ./pro

CMakeLists.txt

CMAKE_MINIMUM_REQUIRED(VERSION 2.20)                            #最低版本要求SET(CMAKE_CXX_COMPILER "g++-11")                                #设置g++编译器set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")                    #添加编译选项PROJECT(CLASS)                                                  #设置工程名MESSAGE(STATUS "class test")                                    #打印消息ADD_EXECUTABLE(pro main.cpp person.cpp man.cpp)                 #生成可执行文件

person.hpp

#ifndef __PERSON_HPP__
#define __PERSON_HPP__#include <iostream>
using namespace std;namespace People
{class Person{public:string name;int age;void print_info();Person();Person(string name,int age);~Person();private:int income;protected:};class person{public:string name;virtual void play() = 0;virtual ~person();};class machine{public:virtual void introduce() = 0;virtual ~machine();};}#endif

person.cpp

#include "person.hpp"
#include <iostream>
using namespace std;void People::Person::print_info()
{cout <<  "name : " <<  this->name << endl;cout <<  "age : " <<  this->age << endl;
}People::Person::Person()
{cout << "Person constructor" <<  endl;
}People::Person::Person(string name,int age):name(name),age(age)
{cout << "user define Person constructor" <<  endl;
}People::Person::~Person()
{cout << "Person destructor" << endl;
}People::person::~person()
{cout << "user define person desturctor" << endl;
}People::machine::~machine()
{cout << "machine virtual function" << endl;
}

man.hpp

#ifndef __MAN_HPP__
#define __MAN_HPP__
#include "person.hpp"class Man:public People::Person
{public:string description;void do_job();void print_info();Man();Man(string name,int age,string description);~Man();private:protected:
};class man:private People::Person
{public:using Person::name;using Person::age;using Person::print_info;
};class gamer:public People::person
{public:void play();gamer();~gamer();
};class sportsman:public People::person
{public:void play();sportsman();~sportsman();
};class robot:public People::machine
{public:void introduce();robot();~robot();
}; #endif

man.cpp

#include "man.hpp"
#include <iostream>
using namespace std;void Man::do_job()
{cout << this->name << " working" << endl;
}void Man::print_info()
{cout << "name :" << this->name << endl;cout << "age :" << this->age << endl;cout << "description :" << this->description << endl;
}void gamer::play()
{cout << this->name << " playing game" << endl;
}gamer::gamer()
{cout << "user define gamer consturctor function" << endl;
}gamer::~gamer()
{cout << "user define gamer desturctor function" << endl;
}sportsman::sportsman()
{cout << "user define sportsman consturctor function" << endl;
}sportsman::~sportsman()
{cout << "user define sportsman desturctor function" << endl;
}void sportsman::play()
{cout << this->name << " playing ping-pong" << endl;
}void robot::introduce()
{cout << "i am robot" << endl;
}robot::robot()
{cout << "robot  consturctor function" << endl;
}robot::~robot()
{cout << "robot  desturctor function" << endl;
}Man::Man()
{cout << "man constructor" << endl;
}Man::Man(string name = "xxx",int age = 0,string description = "xxx"):Person(name,age),description(description)
{cout << "user define  man constructor" << endl;
}Man::~Man()
{cout << "man destructor" << endl;
}

main.cpp

#include "person.hpp"
#include "man.hpp"using namespace People;
using namespace std;int main()
{Man m1;                 //父类构造->子类构造->子类析构->父类析构Man m2("xiaoming",23,"height");m2.print_info();m2.do_job();m2.Person::print_info(); //全域路径访问隐藏父类方法Person p1 = m2;         //子类初始化父类p1.print_info();man m3;m3.name = "xiaohua";m3.age = 27;m3.print_info();        //using放开保护继承(class A :private/protected B)//需要保证抽象基类的析构函数为虚才能正常调用派生类析构函数person *p = new gamer;p->name = "gamer";p->play();delete p;//抽象基类的析构函数是否为虚都能调用派生类析构函数sportsman s;s.name = "sportsman";person *t = &s;t->play();//接口和抽象基类的析构函数一般定义为虚robot r;r.introduce();return 0;
}

结果示例：

 demo4:

        运算符重载

目录：

run.sh

#!/bin/bashif [ -f ./Makefile ]
thenmake clean
ficmake .makeecho "---------------------------------"./pro

check_mem.sh

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --trace-children=yes -s ./pro

clean.sh

#!/bin/bashrm -rf CMakeFiles pro Makefile CMakeCache.txt cmake_install.cmake

CMakeLists.txt

CMAKE_MINIMUM_REQUIRED(VERSION 2.20)                            #最低版本要求SET(CMAKE_CXX_COMPILER "g++-11")                                #设置g++编译器set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")                    #添加编译选项PROJECT(CLASS)                                                  #设置工程名MESSAGE(STATUS "class test")                                    #打印消息ADD_EXECUTABLE(pro main.cpp)                                    #生成可执行文件

main.cpp

#include <iostream>using namespace std;class coordinate
{public:int *px;int *py;coordinate();coordinate(const coordinate &cd);coordinate(int x,int y);~coordinate();void print_coordinate();coordinate operator+(const coordinate & other);coordinate operator=(const coordinate & other);coordinate operator++(int x);           //i++coordinate operator++(void);            //++ibool operator==(const coordinate & other);friend void operator+=(coordinate & a,const coordinate & b);    //友元函数只能传参方式调用类成员
};coordinate::coordinate()
{this->px = new int(0);this->py = new int(0);
}coordinate::coordinate(int x,int y)
{this->px = new int(x);this->py = new int(y);
}coordinate::coordinate(const coordinate &cd)
{cout << "copy" << endl;this->px = new int(*(cd.px));this->py = new int(*(cd.py));
}coordinate::~coordinate()
{delete this->px;delete this->py;
}void coordinate::print_coordinate()
{cout << "(" << *(this->px) << "," << *(this->py) << ")" << endl;return;
}coordinate  coordinate::operator+(const coordinate & other)
{cout << "+" << endl;coordinate tmp;*(tmp.px) = *(this->px) + *(other.px);*(tmp.py) = *(this->py) + *(other.py);return tmp;
}coordinate  coordinate::operator=(const coordinate & other)
{cout << "=" << endl;if(this != &other){*(this->px) = *(other.px);*(this->py) = *(other.py);}return *this;
}coordinate  coordinate::operator++(void)
{*(this->px) += 1;*(this->py) += 1;return *this;
}coordinate  coordinate::operator++(int x)
{coordinate tmp;*(tmp.px) = *(this->px);*(tmp.py) = *(this->py);*(this->px) += 1;*(this->py) += 1;return tmp;
}void operator+=(coordinate & a,const coordinate & b)
{*(a.px) += *(b.px);*(a.py) += *(b.py);return;
}bool coordinate::operator==(const coordinate & other)
{if(*(this->px) == *(other.px) && *(this->py) == *(other.py))return true;return false;
}int main()
{coordinate c1(1,1);coordinate c2(2,2);cout << "------------3" << endl;coordinate c3;c3 = c1 + c2;                   //先定义再赋值时,先调用加法,在调用自定义=,在调用自定义拷贝(深浅拷贝均相同,浅拷贝时若为定义=和拷贝,则调用默认)c3.print_coordinate();cout << "------------4" << endl;coordinate c4 = c1 + c2;        //只调用+(深浅拷贝均相同)c4.print_coordinate();cout << "------------5" << endl;coordinate c5 = c1;             //调用自定义拷贝(浅拷贝调用默认)c5.print_coordinate();cout << "------------6" << endl;coordinate c6(c1);              //调用自定义拷贝(浅拷贝调用默认)c6.print_coordinate();cout << "tmp------------7" << endl;coordinate tmp;coordinate c7;tmp = c7++;tmp.print_coordinate();cout << "tmp------------8" << endl;coordinate c8;tmp = ++c8;tmp.print_coordinate();cout << "------------9" << endl;coordinate c9(1,1);operator+=(c9,c9);c9.print_coordinate();cout << "------------10" << endl;coordinate c10(1,1);bool res = (c10 == c1);cout << boolalpha << res << endl;return 0;
}

结果示例：

 

demo5:

        类静态成员

目录：

 run.sh

#!/bin/bashif [ -f ./Makefile ]
thenmake clean
ficmake .makeecho "---------------------------------"./pro

clean.sh

#!/bin/bashrm -rf CMakeFiles pro Makefile CMakeCache.txt cmake_install.cmake

check_mem.sh

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --trace-children=yes -s ./pro

CMakeLists.txt

CMAKE_MINIMUM_REQUIRED(VERSION 2.20)                            #最低版本要求SET(CMAKE_CXX_COMPILER "g++-11")                                #设置g++编译器set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")                    #添加编译选项PROJECT(CLASS)                                                  #设置工程名MESSAGE(STATUS "class test")                                    #打印消息ADD_EXECUTABLE(pro main.cpp)                                    #生成可执行文件

main.cpp

#include <iostream>using namespace std;class Person
{public:string name;Person();Person(string name);static int objetcion_num;static void print_obj_num();static void print_name(string name);    //静态方法传参访问非静态成员};//静态类
class constant
{public:static int week_day_num;        //一周的天数static int earth_radius;        //地球半径static void print_info();
};int constant::week_day_num = 7;
int constant::earth_radius = 6371;void constant::print_info()
{cout << "days of the week :" << constant::week_day_num << endl;cout << "radius of the earth :" << constant::earth_radius << endl;
}int Person::objetcion_num = 0;    //<==>int objetcion_num;//类中静态成员的访问方式
Person::Person()
{objetcion_num++;
}Person::Person(string name)
{this->name = name;this->objetcion_num++;
}void Person::print_obj_num()
{cout << "obj_num :" << Person::objetcion_num << endl;
}void Person::print_name(string name)
{cout << "person name :" << name << endl;
}int main()
{//类外静态成员的访问方式Person p1;cout << "obj_num :" << p1.objetcion_num << endl;Person p2("xaioming");cout << "obj_num :" << Person::objetcion_num << endl;Person p3("xaiohua");p3.print_obj_num();constant::print_info();return 0;
}

结果示例：

 

demo6:

        友元函数，友元类

目录：

run.sh

#!/bin/bashif [ -f ./Makefile ]
thenmake clean
ficmake .makeecho "---------------------------------"./pro

check_mem.sh

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --trace-children=yes -s ./pro

clean.sh

#!/bin/bashrm -rf CMakeFiles pro Makefile CMakeCache.txt cmake_install.cmake

CMakeLists.txt

CMAKE_MINIMUM_REQUIRED(VERSION 2.20)                            #最低版本要求SET(CMAKE_CXX_COMPILER "g++-11")                                #设置g++编译器set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")                    #添加编译选项PROJECT(CLASS)                                                  #设置工程名MESSAGE(STATUS "class test")                                    #打印消息ADD_EXECUTABLE(pro main.cpp)                                    #生成可执行文件

main.cpp

#include <iostream>using namespace std;//前置申明解决友元类未定义
class Father;
class Son;class Father
{public:string name;int age;Father();Father(string name,int age);void print_name(string name);friend  class Son;
};class Son
{public:string name;int age;Son();Son(string name,int age);void print_age(int age);friend class Father;};Father::Father(string name,int age)
{this->name = name;this->age = age;
}void Father::print_name(string name)
{cout << name << endl;
}Son::Son(string name,int age)
{this->name = name;this->age = age;
}void Son::print_age(int age)
{cout << age << endl;
}int main()
{Father f("xiaoming",40);Son s("xiaohua",20);f.print_name(s.name);s.print_age(f.age);return 0;
}

 结果示例：