This message is sent to an I/O procedure by mmioWrite to request that data be written to an open file and then that any internal buffers used by the I/O procedure be flushed to disk.
LONG lParam1
Specifies a huge pointer to a buffer containing the data to write to the file.
LONG lParam2
Specifies the number of bytes to write to the file.
The return value is the number of bytes actually written to the file. If there is an error, the return value is -1.
The I/O procedure is responsible for updating the lDiskOffset field of the MMIOINFO structure to reflect the new file position after the write operation.
Note that this message is equivalent to the MMIOM_WRITE message except that it additionally requests that the I/O procedure flush its internal buffers, if any. Unless an I/O procedure performs internal buffering, this message can be handled exactly like the MMIOM_WRITE message.
mmioWrite, mmioFlush, MMIOM_READ, MMIOM_WRITE