mmioInstallIOProc function

The mmioInstallIOProc function installs or removes a custom I/O procedure. This function also locates an installed I/O procedure, using its corresponding four-character code.


LPMMIOPROC mmioInstallIOProc(
  FOURCC     fccIOProc,
  DWORD      dwFlags



Four-character code identifying the I/O procedure to install, remove, or locate. All characters in this code should be uppercase.


Pointer to the I/O procedure to install. To remove or locate an I/O procedure, set this parameter to NULL. For more information about the I/O procedure, see MMIOProc.


Flag indicating whether the I/O procedure is being installed, removed, or located. The following values are defined.

Value Meaning
MMIO_FINDPROC Searches for the specified I/O procedure.
MMIO_GLOBALPROC This flag is a modifier to the MMIO_INSTALLPROC flag and indicates the I/O procedure should be installed for global use. This flag is ignored if MMIO_FINDPROC or MMIO_REMOVEPROC is specified.
MMIO_INSTALLPROC Installs the specified I/O procedure.
MMIO_REMOVEPROC Removes the specified I/O procedure.

Return value

Returns the address of the I/O procedure installed, removed, or located. Returns NULL if there is an error.


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