The OVERLAPPED structure contains the information used in compelled (asynchronous) I/O mode.
The OVERLAPPED structure contains the following members:
DWORD Internal - reserved to be used by the operation system. This member defines the state dependent of the system and is valid when the GetOverlappedResult function is returned without the ERROR_IO_PENDING enhanced error parameter.
DWORD InternalHigh - reserved to be used by the operation system. Ths member defines the length of the transmitted data and is valid when the GetOverlappedResult function returns TRUE.
DWORD Offset - detection of the file position before the transmittion is started. File position is byte shift from the file beginning. The request process places this member before calling ReadFile or WriteFile functions. when reading from or writing into communication devices.
DWORD OffsetHigh - detection of the beginning position of the byte shift to start transmission. This member is ignored when reading from or writing into communication devices.
HANDLE hEvent - identification of the events set for the status signal when the transmittion ends. The request process sets this member before calling ReadFile, WriteFile, ConnectNamedPipe or TransactNamedPipe functions.
You can use the HasOverlappedIoCompleted macro to detect whether the asynchronous I/O operation is over. The CancelIo function can be used to cancel the asynchronous I/O operation.
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