title: index or position in std::set
body: <p>I have a std::set of std::string. I need the "index" or "position" of each string in the set, is this a meaningful concept in the context?</p>
  
  <p>I guess find() will return an iterator to the string, so my question might be better phrased as : "How do I convert an iterator to a number?". </p>