LPOVERLAPPED_COMPLETION_ROUTINE Function Pointer
Points to a function that notifies the host when an overlapped (that is, asynchronous) I/O to a device has completed.
typedef VOID (*LPOVERLAPPED_COMPLETION_ROUTINE) ( [in] DWORD dwErrorCode, [in] DWORD dwNumberOfBytesTransfered, [in] LPVOID lpOverlapped );
[in] A value that is an error code if the device has been closed; otherwise, this value is zero.
Closing a device causes all pending I/O to the device to be completed immediately.
[in] The number of bytes transferred by the I/O operation.
[in] A pointer to a structure that contains information to be used to complete the I/O request.