C++学习（四）

对象继承

#include <iostream>
using namespace std;

class Person{
public:
    int age;
    char * name;
    Person(char * name, int age){}
};
//类默认是私有的
//public：公开继承,不加public会导致 main()函数中 student.age无法引用
//private: 私有继承在类里面是可以拿到父类属性，但是在类外边不行
class Student : public Person{
public:
    Student(char * name, int age): Person(name,age){}
};


int main(){
    Student student("王三",10);
    student.age = 20;
    cout <<  "age :"<< student.age <<endl;
    return 0;
}

多继承

c++中多继承存在二义性问题。例如：

 

#include <iostream>

using namespace std;

class BaseActivity1 {
public:
    BaseActivity1(){}
    void showInfo(){
        cout << " BaseActivity1 showInfo" <<endl;
    }
};

class BaseActivity2{
public:
    BaseActivity2(){}
    void showInfo(){
        cout << " BaseActivity2 showInfo" <<endl;
    }
};

class MainActivity :public BaseActivity1,public BaseActivity2{
    //解决方案2
  // void showInfo(){
 //       cout << " MainActivity showInfo" <<endl;
  //  }
};


int main(){
    MainActivity act;
    //此行代码会报错，编译器不清楚到底执行的是base1还是base2的showInfo()
   // act.showInfo();
   //解决方案1：指定父类的执行函数 low
   act.BaseActivity1::showInfo();
   //方案2：可在子类中重写此函数
   
    return  0;
}

 

虚继承（系统源码推荐使用）

virtual： 虚关键字

A为顶层父类，B C 继承A， D继承B C。

#include <iostream>

using namespace std;

class Person{
public:
    int age;
};
class Women :public Person{

};

class Men : public Person{
    
};

class Student :public Women,public Men{
//第二种解决方案：子类重写
public:
    int age;
};


int main(){
    Student student;
    //第一种解决方案
    student.Women::age = 100;
    cout << "age: "<< student.Women::age << endl;
    return  0;
}


第3种解决方案：通过virtual 关键字()
#include <iostream>

using namespace std;

class Person{
public:
    int age;
};
//通过virtual 关键字
class Women :virtual public Person{

};

class Men : virtual public Person{

};

class Student :public Women,public Men{

};


int main(){
    Student student;
    student.age = 100;
    cout <<"age  " << student.age <<endl;
    return  0;
}