OVERLAPPED

The OVERLAPPED structure contains information used in asynchronous input and output (I/O).

typedef struct _OVERLAPPED { 
    ULONG_PTR  Internal; 
    ULONG_PTR  InternalHigh; 
    DWORD  Offset; 
    DWORD  OffsetHigh; 
    HANDLE hEvent; 
} OVERLAPPED; 

Members

Internal

Reserved for operating system use. This member, which specifies a system-dependent status, is valid when the GetOverlappedResult function returns without setting the extended error information to ERROR_IO_PENDING.

InternalHigh

Reserved for operating system use. This member, which specifies the length of the data transferred, is valid when the GetOverlappedResult function returns TRUE.

Offset

Specifies a file position at which to start the transfer. The file position is a byte offset from the start of the file. The calling process sets this member before calling the ReadFile or WriteFile function. This member is ignored when reading from or writing to named pipes and communications devices and should be zero.

OffsetHigh

Specifies the high word of the byte offset at which to start the transfer. This member is ignored when reading from or writing to named pipes and communications devices and should be zero.

hEvent

Handle to an event set to the signaled state when the operation has been completed. The calling process must set this member either to zero or a valid event handle before calling any overlapped functions. To create an event object, use the CreateEvent function.

Remarks

You can use the HasOverlappedIoCompleted macro to determine whether an asynchronous I/O operation has completed. You can use the CancelIo function to cancel an asynchronous I/O operation.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winbase.h; include Windows.h.

See Also

Synchronization Overview, Synchronization Structures, CancelIo, GetOverlappedResult, HasOverlappedIoCompleted, ReadFile, WriteFile