同名静态成员

#include <iostream>

class Person
{
public:
   static int age;
};

class Student: public Person
{
public:
   static int age;
   int grade;
};

int Person::age = 5;
int Student::age = 15;

int main()
{
   using namespace std;

   Student s;
   cout << "age " << s.age << endl;
   cout << "Person::age " << s.Person::age << endl;

   cout << "age " << Student::age << endl;
   cout << "Person::age " << Student::Person::age << endl;

   return 0;
}

$ ./a.out       
age 15
Person::age 5
age 15
Person::age 5