title: Addition some interval to tm structs
body: <p>I have one struct <em>tm</em>.<br>
  And I need to add some fixed interval (given in xx years, xx months, xx days)
  to the <em>tm</em> struct.<br>
  Is there any standard function to do this?</p>
  
  <p>The compiler I use is MSVC 2005 on Windows XP.</p>