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The MMIOM_READ message is sent to an I/O procedure by the mmioRead function to request that a specified number of bytes be read from an open file.
MMIOM_READ lParam1 = (LPARAM) lBuffer lParam2 = (LPARAM) cbRead
lBuffer
Address of the buffer to be filled with data read from the file.
cbRead
Number of bytes to read from file.
Returns the number of bytes actually read from the file. If no more bytes can be read, the return value is 0. If there is an error, the return value is - 1.
The I/O procedure is responsible for updating the lDiskOffset member of the MMIOINFO structure to reflect the new file position after the read operation.