title: how to handle nested comment in flex
body: <p>I am working on writing a flex scanner for a language supporting nested comment like this:</p>
  
  <pre><code>/*
  /**/
  */
  </code></pre>
  
  <p>I use to work on ocaml/ocamllex that support recursive calling lex scanner very elegent. But I am now switching to c++/flex, how to handle such nested comment?</p>