Polymorphism

#include <iostream>
#include <vector>

using namespace std;

struct Base {
  int av;
  virtual bool is (int value) const
  {
    return av == value;
  }
  virtual void print() const
  {
    cout << av << endl;
  }
};

struct A : public Base {
  int bv;
  virtual bool is (int value) const
  {
    return bv == value;
  }
  virtual void print () const
  {
    cout << bv << endl;
  }
};
struct database {
  vector <Base*> basev;
  Base NBase;

  database () { NBase.av = 0; }

  Base* findb (int value) {
    for (int i = 0; i < basev.size (); ++i) {
      if(basev[i]->is (value));
    return basev[i];
    }
    return &NBase;
  }
} db;

int main( ) {

  Base der;
  der.av = 5;
  db.basev.push_back (&der);

  Base* found = db.findb (5);
  found->print ();
}