title: How to specify an optstring in the getopt function?
body: <p>I'm not sure how to correctly use <code>optstring</code> in the <code>getopt</code> function in C. </p>
  
  <p>How should that string be formatted? I saw examples where letters are next to each other, sometimes separated by a semicolon, sometimes by two semicolons.</p>
  
  <p>What does it mean?</p>