Base *pA = new Descendant_G2();
    Base *pA2 = new Descendant();
    Descendant * pb = dynamic_cast<Descendant *>(pA);
    if (pb)
        pb->f3();
    Descendant_G2 * pc = dynamic_cast<Descendant_G2 *>(pA2);
    if (pc)
        pc->f3();
    delete pA;
    delete pA2;