title: How to use `strtoul` to parse string where zero may be valid?
body: <p>According to the documentation for <code>strtoul</code>, regarding its return value...</p>
  
  <blockquote>
    <p>This function returns the converted integral number as a long int value. If no valid conversion could be performed, a zero value is returned.</p>
  </blockquote>
  
  <p>What if I'm parsing a user-supplied string of "0" where, for my application, "0" may be a valid entry?  In that case it seems that I have no way to determine from using <code>strtoul</code> if a valid conversion was performed.  Is there another way to handle this?</p>