The following example illustrates the the entry point used to access the functionality of an I/O procedure.
LONG APIENTRY IOProc_Entry ( PVOID pmmioStr,
USHORT usMessage,
LONG lParam1,
LONG lParam2)
Associated parameters include the following.
┌───────────────┬─────────────────────────────────────────────┐ │Parameter │Description │ ├───────────────┼─────────────────────────────────────────────┤ │PVOID pmmioStr │Specifies a pointer to an MMIOINFO data │ │ │structure that contains information about the│ │ │open file. │ ├───────────────┼─────────────────────────────────────────────┤ │USHORT usMsg │Specifies the message that the file I/O │ │ │procedure is being asked to process. │ │ │(User-defined messages must have messages │ │ │defined above MMIOM_USER.) │ ├───────────────┼─────────────────────────────────────────────┤ │LONG lParam1 │Specifies message-dependent information such │ │ │as a file name. │ ├───────────────┼─────────────────────────────────────────────┤ │LONG lParam2 │Specifies additional message-dependent │ │ │information. (Used with some messages as │ │ │values.) │ └───────────────┴─────────────────────────────────────────────┘
Note: The return value is message-dependent. If the I/O procedure does not recognize a message passed in by usMsg, and the default message handler does not recognize usMsg, then it must return MMIOERR_UNSUPPORTED_MESSAGE.