hmmio (HMMIO) - input

      The open file handle returned by mmioOpen.

    usMsg (USHORT) - input

      A message number. See MMIO Messages.

    lParam1 (LONG) - input

      Specifies additional message information. If lParam1 for the particular MMIO message being sent is not a LONG value, cast the value into a LONG data type.

    lParam2 (LONG) - input

      Specifies additional message information. If lParam2 for the particular MMIO message being sent is not a LONG value, cast the value into a LONG data type.

    rc (LONG) - returns

      The return code is specific to the message sent. This includes both successful and failed returns.

      Regarding message-specific return codes, additional information may be contained in the ulErrorRet field of the MMIOINFO structure. This is accessed by called mmioGetLastError.

      MMIO_ERROR

        The message cannot be routed to an IOProc. The handle might be invalid.
      MMIOERR_UNSUPPORTED_MESSAGE
        The I/O procedure does not support the message.

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