title: Function call operator
body: <blockquote>
    <p><strong>Possible Duplicates:</strong><br>
    <a href="https://stackoverflow.com/questions/356950/c-functors-and-their-uses">C++ Functors - and their uses.</a><br>
    <a href="https://stackoverflow.com/questions/317450/why-override-operator">Why override operator() ?</a>  </p>
  </blockquote>
  
  
  
  <p>I've seen the use of <code>operator()</code> on STL containers but what is it and when do you use it?</p>