The following code illustrates how to send a message to the IOProc.

   HMMIO hmmio1;
   USHORT usMsg;
   LONG lParam1 = 0L;
   LONG lParam2 = 0L;
   LONG rc;

    ...

   usMsg = MMIOM_GETCF;

   rc = mmioSendMessage(hmmio1, usMsg, lParam1, lParam2);

   if (!rc)
     /* error */
   else
    ...