e difficult or impossible
      to call a C function, especially if the interface to that C function
      is not under the control of the user.
    </p>

    <p>
      Some reference books discuss this topic by showing little isolated
      pieces of code, which do not form a real program, and cannot actually
      be compiled or used.  Since EVERYTHING has to be correctly written and
      working properly together to make this delicate operation happen, it
      is very important to have an entire calcul