c++ 虚函数

#include<iostream>
using namespace std;
class A
{
    public:
    void print()
    {
        cout<<"This is A"<<endl;
    }
};
 
class B : public A
{
    public:
    void print()
    {
        cout<<"This is B"<<endl;
    }
};
 
int main()
{
    //为了在以后便于区分，我这段main()代码叫做main1
    A a;
    B b;
    a.print();
    b.print();
    return 0;
}

让后是

#include<iostream>
using namespace std;

class A
{
    public:
    virtual void print()
    {
        cout<<"This is A"<<endl;
    }
};
 
class B : public A
{
    public:
    void print()
    {
        cout<<"ThisisB"<<endl;
    }
};
 
int main()
{
    //为了在以后便于区分，我这段main()代码叫做main1
    A a;
    B b;
    a.print();
    b.print();
    return 0;
}

其中b中的virtual可以省略，但是仍然是虚函数