The following code illustrates how to set the buffer.

   HMMIO hmmio1;
   LONG cchBuffer;
   PCHAR pchBuffer;
   USHORT usFlags = 0;
   USHORT rc;

    ...

   pchBuffer = NULL;
   cchBuffer = 0L;

   rc = mmioSetBuffer(hmmio1, pchBuffer, cchBuffer, usFlags);

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