title: Where does getopt_long store an unrecognized option?
body: <p>When <code>getopt</code> or <code>getopt_long</code> encounters an illegal option, it stores the offending option character in <code>optopt</code>. When the illegal option is a <em>long</em> option, where can I find out what the option was? And does anything meaningful get stored in <code>optopt</code> then?</p>
  
  <p>I've set <code>opterr = 0</code> to suppress the automatically printed error message. I want to create my own message that I can print or log where I'd like, but I want to include the name of the unrecognized option.</p>