第45课 继承中的访问级别

#include <iostream>
using namespace std;

class Parent
{
protected:    //在子类中可以直接访问
    int m_a;
protected:
    int m_b;
public:
    int m_c;
    
    void set(int a, int b, int c)
    {
        m_a = a;
        m_b = b;
        m_c = c;
    }
};

//冒号：表示继承关系,public表示继承方式，Parent为父类
class Child_A : public Parent  //public继承
{
public:
    void print()
    {
        cout << "m_a = " << m_a << endl;
        cout << "m_b = " << m_b << endl;
        cout << "m_c = " << m_c << endl;
    }    
};

class Child_B : protected Parent //protected继承
{
public:
    void print()
    {
        cout << "m_a = " << m_a << endl;
        cout << "m_b = " << m_b << endl;
        cout << "m_c = " << m_c << endl;
    }    
};

class Child_C : private Parent //protected继承
{
public:
    void print()
    {
        cout << "m_a = " << m_a << endl;
        cout << "m_b = " << m_b << endl;
        cout << "m_c = " << m_c << endl;
    }    
};

int main()
{
    Child_A a;
    Child_B b;
    Child_C c;
    
    a.m_c = 100; //合法
    //b.m_c = 100; //Child_B，protected继承自parent，所以来自父类的公有成员m_c
                 //变成了protected属性，外界无法访问
    //c.m_c = 100; //Child_C，private继承自parent，所以来自父类的成员m_c
                 //变成了private属性，外界无法访问

    a.set(1, 1, 1); //合法
    //b.set(2, 2, 2); //继承方式为protected，来自父类的函数set无法被外界访问
    //c.set(3, 3, 3); //继承方式为private，来自父类的函数set无法被外界访问 
    
    a.print();
    b.print();
    c.print();
    
    return 0;
}