The application should call MIDIQueryNumClasses to retrieve the number of node classes currently registered and initialize ulNumClasses with this value (to determine the size of the paClassInfo array).
A Type B driver can register or deregister classes at any time, usually at the prompting of another RTMIDI application. Therefore, an application should be prepared to refresh its list of class names. For simplicity, the application can provide a user-driven method to perform the refresh.