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midiOutCachePatches function

The midiOutCachePatches function requests that an internal MIDI synthesizer device preload and cache a specified set of patches.


MMRESULT midiOutCachePatches(
   HMIDIOUT hmo,
   UINT     wBank,
   WORD     *lpPatchArray,
   UINT     wFlags



Handle to the opened MIDI output device. This device must be an internal MIDI synthesizer. This parameter can also be the handle of a MIDI stream, cast to HMIDIOUT.


Bank of patches that should be used. This parameter should be set to zero to cache the default patch bank.


Pointer to a PATCHARRAY array indicating the patches to be cached or uncached.


Options for the cache operation. It can be one of the following flags.

Value Meaning
MIDI_CACHE_ALLCaches all of the specified patches. If they cannot all be cached, it caches none, clears the PATCHARRAY array, and returns MMSYSERR_NOMEM.
MIDI_CACHE_BESTFITCaches all of the specified patches. If they cannot all be cached, it caches as many patches as possible, changes the PATCHARRAY array to reflect which patches were cached, and returns MMSYSERR_NOMEM.
MIDI_CACHE_QUERYChanges the PATCHARRAY array to indicate which patches are currently cached.
MIDI_UNCACHEUncaches the specified patches and clears the PATCHARRAY array.


Return value

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

Return codeDescription

The flag specified by wFlags is invalid.


The specified device handle is invalid.


The array pointed to by lpPatchArray is invalid.


The device does not have enough memory to cache all of the requested patches.


The specified device does not support patch caching.



Some synthesizers are not capable of keeping all patches loaded simultaneously and must load data from disk when they receive MIDI program change messages. Caching patches ensures that the specified patches are immediately available.

Each element of the PATCHARRAY array represents one of the 128 patches and has bits set for each of the 16 MIDI channels that use the particular patch. The least-significant bit represents physical channel 0, and the most-significant bit represents physical channel 15 (0x0F). For example, if patch 0 is used by physical channels 0 and 8, element 0 would be set to 0x0101.

This function applies only to internal MIDI synthesizer devices. Not all internal synthesizers support patch caching. To see if a device supports patch caching, use the MIDICAPS_CACHE flag to test the dwSupport member of the MIDIOUTCAPS structure filled by the midiOutGetDevCaps function.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]


Mmsystem.h (include Windows.h)





See also

MIDI Functions