title: detecting no argument with getopt_long
body: <p>How do I detect the user passed no arguments to a program with getopt_long? I could detect the user calling the program with no arguments by checking argc, but what about the user calling my program with just a dash?</p>
  
  <pre><code>$ my_prog -
  </code></pre>
  
  <p>Do I need to include this option somehow in my getopt statement?</p>
  
  <pre><code>while(ca = getopt_long(argc, argv, "abc:D:",...)
  </code></pre>
  
  <p>What would the function return?</p>