title: What exactly is the first argument of select() function
body: <p>I don't quite understand the purpose of the first argument in the <code>select</code> function.<a href="http://en.wikipedia.org/wiki/Select_%28Unix%29" rel="noreferrer"> Wikipedia</a> describes it as the maximum file descriptor across all the sets, plus 1 . Why +1 and why does <code>select</code> need this information ?</p>