title: utc seconds since midnight to datetime
body: <p>I'm getting radar data as "tracks" and the track data indicates the number of UTC seconds since the last midnight, apparently. This is not the number of seconds since the 1st of jan 1970.</p>
  
  <p>Now I want to convert that to date time, knowing that the clock on the computer could be slightly out of sync with the clock on the radar. I'll assume the radar's seconds are the reference, not the computer's.
  I want to convert these  seconds  to a full date time. Things seem to be a little tricky around
  midnight. </p>
  
  <p>Any suggestions? I've got some ideas, but I don't want to miss anything.</p>
  
  <p>I'm working with C++ Qt.</p>