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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


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

  • pIOProc
    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.

  • dwFlags
    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]


Mmsystem.h (include Windows.h)





Unicode and ANSI names

mmioInstallIOProcW (Unicode) and mmioInstallIOProcA (ANSI)