midiOutUnprepareHeader function (mmeapi.h)

Article
02/22/2024

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

Syntax

MMRESULT midiOutUnprepareHeader(
  HMIDIOUT  hmo,
  LPMIDIHDR pmh,
  UINT      cbmh
);

Parameters

hmo

Handle to the MIDI output device. This parameter can also be the handle of a MIDI stream cast to HMIDIOUT.

pmh

Pointer to a MIDIHDR structure identifying the buffer to be cleaned up.

cbmh

Size, in bytes, of the MIDIHDR structure.

Return value

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

Return code	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.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	mmeapi.h (include Windows.h)
Library	Winmm.lib
DLL	Winmm.dll