GetOverlappedResult

The GetOverlappedResult function retrieves the results of an overlapped operation on the specified file, named pipe, or communications device.

Windows 95/98: This function works only on communications devices or on files opened by using the DeviceIoControl function.

BOOL GetOverlappedResult(
  HANDLE hFile,                       // handle to file, pipe, or device
  LPOVERLAPPED lpOverlapped,          // overlapped structure
  LPDWORD lpNumberOfBytesTransferred, // bytes transferred
  BOOL bWait                          // wait option
);

Parameters

hFile

[in] Handle to the file, named pipe, or communications device. This is the same handle that was specified when the overlapped operation was started by a call to the ReadFile, WriteFile, ConnectNamedPipe, TransactNamedPipe, DeviceIoControl, or WaitCommEvent function.

lpOverlapped

[in] Pointer to an OVERLAPPED structure that was specified when the overlapped operation was started.

lpNumberOfBytesTransferred

[out] Pointer to a variable that receives the number of bytes that were actually transferred by a read or write operation. For a TransactNamedPipe operation, this is the number of bytes that were read from the pipe. For a DeviceIoControl operation, this is the number of bytes of output data returned by the device driver. For a ConnectNamedPipe or WaitCommEvent operation, this value is undefined.

bWait

[in] Specifies whether the function should wait for the pending overlapped operation to be completed. If TRUE, the function does not return until the operation has been completed. If FALSE and the operation is still pending, the function returns FALSE and the GetLastError function returns ERROR_IO_INCOMPLETE.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The results reported by the GetOverlappedResult function are those of the specified handle's last overlapped operation to which the specified OVERLAPPED structure was provided, and for which the operation's results were pending. A pending operation is indicated when the function that started the operation returns FALSE, and the GetLastError function returns ERROR_IO_PENDING. When an I/O operation is pending, the function that started the operation resets the hEvent member of the OVERLAPPED structure to the nonsignaled state. Then when the pending operation has been completed, the system sets the event object to the signaled state.

Specify a manual-reset event object in the OVERLAPPED structure. If an auto-reset event object is used, the event handle must not be specified in any other wait operation in the interval between starting the overlapped operation and the call to GetOverlappedResult. For example, the event object is sometimes specified in one of the wait functions to wait for the operation's completion. When the wait function returns, the system sets an auto-reset event's state to nonsignaled, and a subsequent call to GetOverlappedResult with the bWait parameter set to TRUE causes the function to be blocked indefinitely.

If the bWait parameter is TRUE, GetOverlappedResult determines whether the pending operation has been completed by waiting for the event object to be in the signaled state.

Windows 95/98: If bWait is TRUE, the hEvent member of the OVERLAPPED structure must not be NULL.

Windows NT/2000: If the hEvent member of the OVERLAPPED structure is NULL, the system uses the state of the hFile handle to signal when the operation has been completed. Use of file, named pipe, or communications-device handles for this purpose is discouraged. It is safer to use an event object because of the confusion that can occur when multiple simultaneous overlapped operations are performed on the same file, named pipe, or communications device. In this situation, there is no way to know which operation caused the object's state to be signaled.

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.
  Library: Use Kernel32.lib.

See Also

Synchronization Overview, Synchronization Functions, CancelIo, ConnectNamedPipe, CreateEvent, DeviceIoControl, GetLastError, OVERLAPPED, ReadFile, TransactNamedPipe, WaitCommEvent, WriteFile