Cpp 知识3
权限对继承的影响
当使用protected继承时，所使用的基类成员时为public会换成protected 再去看下面的protected权限 类内部是可以访问的 但是同一类的对象是不能访问的 同理
#include <iostream>using namespace std;//基类，父类
class Vehicle{//交通工具，车，抽象的概念public:string type;string contry;string color;double price;int numOfWheel;protected:int protectedData;
private:int privateData;public:void run();void stop();};//派生类, 子类
class Roadster : protected Vehicle { //跑车，也是抽象，比父类感觉上范围缩小点 子类：public 父类 （因为或默认private）public:void openTopped(){type="wefrwr"; //在这里type是protected }void pdrifting();};
int main()
{Roadster ftype;ftype.type ="捷豹Ftype"; //这里type是protected 不能在同一类对象中访问return 0;
}
基类/派生类构造函数
Roadster(string contry,double price,int state) :Vehicle(contry,price)
#include <iostream>using namespace std;//基类，父类
class Vehicle{ //交通工具，车，抽象的概念
public:string contry;double price;Vehicle(string contry,double price){cout << "基类的构造函数被调用" << endl;this->contry =contry;this->price = price;}};//派生类，子类
class Roadster : public Vehicle{public:int stateOfTop;Roadster(string contry,double price,int state) :Vehicle(contry,price){cout << "派生类的构造函数被调用" << endl;stateOfTop =state;}};int main()
{Roadster FTYPE("法国",70,0);return 0;
}
虚函数
在C++中，virtual和override 关键字用于支持多态，尤其是在涉及继承和方法重写下的情况下
Virtual关键字
使用场景：在基类中声明虚函数
virtual void func（）
目的：允许派生类重写该函数，实现多态，
class Vehicle{ //交通工具，车，抽象的概念
public:string contry;double price;Vehicle(){};Vehicle(string contry,double price){cout << "基类的构造函数被调用" << endl;this->contry =contry;this->price = price;};//基类中声明了一个虚函数virtual void run(){cout << "车跑起来了" << endl;}};override关键字
使用场景:在基类中重写虚函数
目的：明确指示函数意图重写基类的虚函数
class Bike : public Vehicle{public:void run() override{cout << "脚踩自行车" << endl ;}};#include <iostream>using namespace std;//基类，父类
class Vehicle{ //交通工具，车，抽象的概念
public:string contry;double price;Vehicle(){};Vehicle(string contry,double price){cout << "基类的构造函数被调用" << endl;this->contry =contry;this->price = price;};//基类中声明了一个虚函数virtual void run(){cout << "车跑起来了" << endl;}};//派生类，子类
class Bike : public Vehicle{public:void run() override{cout << "脚踩自行车" << endl ;}};int main()
{Bike b;b.run();return 0;
}
override仅应用于派生类中重写基类的虚函数
如果类中有虚函数，通常应该将析构函数也声明为虚的
一旦在基类中声明为虚函数，该函数在所有派生类中自动成为虚函数，无论是否使用virtual关键字
多重继承
#include <iostream>using namespace std;class classA{
public:void displayA(){cout << "Displaying ClassA" << endl;}void testFunc(){cout << "testFunc ClassA" <<endl;}};class classB{
public:void displayB(){cout << "Displaying classB" << endl;}void testFunc(){cout << "testFunc ClassB" <<endl;}
};class Derived : public classA,public classB{
public:void display(){displayA();displayB();classA::testFunc(); //如果在两个类中有相同的函数 那么应该表明是哪一个类}};int main()
{Derived obj;obj.displayA();obj.displayB();obj.display();return 0;
}
菱形继承
中间的必须采用虚拟继承才可以
class Derived1: virtual public Base
class Derived2: virtual public Base
#include <iostream>using namespace std;class Base{
public:int data;Base(int data){this->data=data;}void pritInfo(){cout << data << endl;}};class Derived1: virtual public Base {//继承自 Base
public:Derived1(int data) : Base(data){}};
class Derived2: virtual public Base {//继承自 Base
public:Derived2(int data) : Base(data){}};class FinalDerived : public Derived1,public Derived2{//继承自 Derived1 和 Derived2
public:FinalDerived(int data) : Base(data),Derived1(data),Derived2(data){}};int main()
{FinalDerived final(10);final.pritInfo();return 0;
}
注意：
FinalDerived(int data) : Base(data),Derived1(data),Derived2(data)
多态
RemoteCon *remoteCon =new TvRemoCon; //多态 向下兼容 remoteCon->openUtils();
#include <iostream>using namespace std;class RemoteCon{
public:virtual void openUtils(){cout <<"遥控器的开被按下" << endl;};};class TvRemoCon : public RemoteCon{public:void openUtils() override{cout << "电视遥控器的开被按下" << endl;}};class RoundspeakerCon : public RemoteCon{public:void openUtils() override{cout << "音响遥控器的开被按下" << endl;}};class lightCon: public RemoteCon{public:void openUtils() override{cout << "灯光遥控器的开被按下" << endl;}
};void test(RemoteCon& r)
{r.openUtils();}
int main()
{RemoteCon *remoteCon =new TvRemoCon; //多态 向下兼容remoteCon->openUtils();RemoteCon *remoteCon2 =new RoundspeakerCon; //多态remoteCon2->openUtils();RemoteCon *remoteCon3 =new lightCon; //多态remoteCon3->openUtils();TvRemoCon tvRemote;test(tvRemote);return 0;
}
结果：
抽象类：
抽象类，不支持被实例化 即派生类不把所有的基类中函数重新定义 那么就会报错
抽象类 也是支持多态的
#include <iostream>using namespace std;class Teacher{public:string name;string school;string major;virtual void goInClass()=0;virtual void startTeaching() =0;virtual void afterTeaching() =0;};
class EnglishTeacher : public Teacher{public:void goInClass() override{cout << "英语老师开始进入教室" << endl;}void startTeaching() override{cout << "英语老师开始教学" << endl ;}void afterTeaching() override{}};int main()
{//Teacher t; //抽象类，不支持被实例化 即派生类不把所有的基类中函数重新定义 那么就会报错EnglishTeacher e;e.goInClass();//抽象类 也是支持多态的Teacher *s = new EnglishTeacher();s->startTeaching();return 0;
}