title: Change format of data in file using boost::regex
body: <p>I have file output.txt, in file we can find something like:</p>
  
  <pre><code>01/01/2015  15:00:00      2222.2222
  2222.2222 2222.2222 2222.2222 
  04/04/2015  15:00:00      2222.2222
  </code></pre>
  
  <p>and i would like to change format from <code>DD/MM/RRRR HH:MM:SS</code> to <code>RRRR-MM-DD HH:MM:SS.000</code> using boost regex. But I have no clue how should I type pattern.</p>
  
  <p>Anyone use boost regex and could help me?</p>