virtual

虚函数提供了动态绑定的特性，父类指针指向子类对象，调用同名函数时，实际执行的是子类函数。

#include <iostream>
#include <string>

using namespace std;

class Person
{
public:
    string name;
    Person(string n) : name(n) {}
    virtual void print()
    {
        cout << "Name: " << name << endl;
    }
};

class Person2
{
public:
    string name;
    Person2(string n) : name(n) {}
    virtual void print() = 0;
};

class Student : public Person
{
public:
    string id;
    Student(string n, string i) : Person(n), id(i) {}
    void print()
    {
        cout << "Name: " << name;
        cout << ". ID: " << id << endl;
    }
};

void printObjectInfo(Person &p)
{
    p.print();
}

int main()
{
    {
        Student stu("yu", "2019");
        printObjectInfo(stu);
    }

    {
        Person *p = new Student("xue", "2020");
        p->print(); // if print() is not a virtual function, different output
        delete p;   // if its destructor is not virtual
    }

    { // if you want to call a function in the base class
        Student stu("li", "2021");
        stu.Person::print();

        Person *p = new Student("xue", "2020");
        p->Person::print();
        delete p;
    }

    return 0;
}