C+继承之同名覆盖,函数重写与多态详解

#include<iostream>
using namespace std;
class Base
{
public:
    int m_data;
    Base():m_data(1)//父类初始化为1
    {  }
};
class Derived : public Base
{
public:
    int m_data;
    Derived():m_data(2)//子类初始化为2
    {  }
};
int main()
{
    Derived d;
    //父类的m_data被隐藏了，但仍存在，可以通过::符访问
    cout<<"base data: "<<d.Base::m_data<<endl;
    //直接访问m_data得到的是子类成员的值
    cout<<"derived data: "<<d.m_data<<endl;
    //验证两个int刚好是8字节，说明d对象有两个整型数
    cout<<sizeof(d)<<endl;
    return 0;
}

#include<iostream>
using namespace std;
class Base
{
public:
    void print()
    {
        cout<<"Base class"<<endl;
    }
};
class Derived : public Base
{
public:
    void print()
    {
        cout<<"Derived class"<<endl;
    }
};
int main()
{
    Derived d;
    d.Base::print();//父类函数被隐藏
    d.print();
    return 0;
}

void how_to_print(Base* p)
{
    p->print();//期望根据对象选择相应函数，不能实现
}
int main()
{
    Base b;
    Derived d;
    how_to_print(&b);
    how_to_print(&d);
    return 0;
}

class Base
{
public:
    virtual void print()//加virtual变成了虚函数
    {
        cout<<"Base class"<<endl;
    }
};