test.cc

#include <iostream>
using namespace std;

class TEST1{
  typedef int id;
public:
  A(){};
  void set(id n){
    x = n;
  };
  void show(){
    cout << x << endl;
  };
  id x;
};

class TEST2 : public TEST1{
  typedef string id;
public:
  B(){};
};

int main(){
  TEST1 test1;
  test1.set(100);
  test1.show();

  TEST2 test2;
  test2.set("100");
  test2.show();
}