midiOutUnprepareHeader

The midiOutUnprepareHeader function cleans up the preparation performed by the midiOutPrepareHeader function. 

MMRESULT midiOutUnprepareHeader(
  HMIDIOUT hmo,            
  LPMIDIHDR lpMidiOutHdr,  
  UINT cbMidiOutHdr        
);

Parameters

hmo
Handle of the MIDI output device. This parameter can also be the handle of a MIDI stream cast to HMIDIOUT.
lpMidiOutHdr
Address of a MIDIHDR structure identifying the buffer to be cleaned up.
cbMidiOutHdr
Size, in bytes, of the MIDIHDR structure.

Return Values

Returns MMSYSERR_NOERROR if successful or an error otherwise. Possible error values include the following:

Value Description
MIDIERR_STILLPLAYING The buffer pointed to by lpMidiOutHdr is still in the queue.
MMSYSERR_INVALHANDLE The specified device handle is invalid.
MMSYSERR_INVALPARAM The specified pointer or structure is invalid.

Remarks

This function is complementary to the midiOutPrepareHeader function. You must call midiOutUnprepareHeader before freeing the buffer. After passing a buffer to the device driver with the midiOutLongMsg function, you must wait until the device driver is finished with the buffer before calling midiOutUnprepareHeader.

Unpreparing a buffer that has not been prepared has no effect, and the function returns MMSYSERR_NOERROR.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in mmsystem.h.
  Import Library: Use winmm.lib.

See Also

Musical Instrument Digital Interface (MIDI) Overview, MIDI Functions, midiOutPrepareHeader, MIDIHDR, midiOutLongMsg