title: How can I determine the maximum value of a pid_t?
body: <p>How can I portably determine the maximum value of the <code>pid_t</code> type?  There's no PID_MAX constant on my system.</p>
  
  <p>(Note, I mean the maximum value permitted by the data type, not the <em>de facto</em> maximum value the system will assign to processes.)</p>
  
  <p><strong>Use case:</strong> I'm converting a user-supplied string specification of a pid to a <code>pid_t</code>, and want to make sure the user's input doesn't exceed the type's capacity.</p>