GetOverlappedResult function (ioapiset.h)

Article
09/23/2022

Retrieves the results of an overlapped operation on the specified file, named pipe, or communications device. To specify a timeout interval or wait on an alertable thread, use GetOverlappedResultEx.

Syntax

BOOL GetOverlappedResult(
  [in]  HANDLE       hFile,
  [in]  LPOVERLAPPED lpOverlapped,
  [out] LPDWORD      lpNumberOfBytesTransferred,
  [in]  BOOL         bWait
);

Parameters

[in] hFile

A 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 any of the following functions:

[in] lpOverlapped

A pointer to an OVERLAPPED structure that was specified when the overlapped operation was started.

[out] lpNumberOfBytesTransferred

A 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.

[in] bWait

If this parameter is TRUE, and the Internal member of the lpOverlapped structure is STATUS_PENDING, the function does not return until the operation has been completed. If this parameter is FALSE and the operation is still pending, the function returns FALSE and the GetLastError function returns ERROR_IO_INCOMPLETE.

Return value

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.

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.

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.

Examples

For an example that uses GetOverlappedResult, see Testing for the End of a File

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Target Platform	Windows
Header	ioapiset.h (include Windows.h on Windows Server 2003, Windows Vista, Windows 7, Windows Server 2008 Windows Server 2008 R2)
Library	Kernel32.lib
DLL	Kernel32.dll

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