title: Formatting the string YYYYMMDD as YYYY.MM.DD using Boost
body: <p>I have a <code>std::string</code> such as <code>20040531</code>, I want to format this as <code>2004.05.31</code>. </p>
  
  <p>Apart from the straight forward way of doing an <code>std::insert</code> at respective locations, is there a better way to do this using Boost? </p>
  
  <p>PS. I cannot use other Boost calls to get date/time as this string is returned via a custom API. So this question is reduced to basic string formatting which may not sound exciting, but I am trying to learn Boost.</p>