The WaitCommEvent function waits for an event to occur for a specified communications device. The set of events that are monitored by this function is contained in the event mask associated with the device handle.
BOOL WaitCommEvent(
HANDLE hFile, // handle to communications device
LPDWORD lpEvtMask, // pointer to variable to receive event
LPOVERLAPPED lpOverlapped, // pointer to overlapped structure
);
| Value | Meaning |
|---|---|
| EV_BREAK | A break was detected on input. |
| EV_CTS | The CTS (clear-to-send) signal changed state. |
| EV_DSR | The DSR (data-set-ready) signal changed state. |
| EV_ERR | A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY. |
| EV_RING | A ring indicator was detected. |
| EV_RLSD | The RLSD (receive-line-signal-detect) signal changed state. |
| EV_RXCHAR | A character was received and placed in the input buffer. |
| EV_RXFLAG | The event character was received and placed in the input buffer. The event character is specified in the device's DCB structure, which is applied to a serial port by using the SetCommState function. |
| EV_TXEMPTY | The last character in the output buffer was sent. |
If hFile was opened with FILE_FLAG_OVERLAPPED, the lpOverlapped parameter must not be NULL. It must point to a valid OVERLAPPED structure. If hFile was opened with FILE_FLAG_OVERLAPPED and lpOverlapped is NULL, the function can incorrectly report that the operation is complete.
If hFile was opened with FILE_FLAG_OVERLAPPED and lpOverlapped is not NULL, WaitCommEvent is performed as an overlapped operation. In this case, the OVERLAPPED structure must contain a handle to a manual-reset event object (created by using the CreateEvent function).
If hFile handle was not opened with FILE_FLAG_OVERLAPPED, WaitCommEvent does not return until one of the specified events or an error occurs.
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.
The WaitCommEvent function monitors a set of events for a specified communications resource. To set and query the current event mask of a communications resource, use the SetCommMask and GetCommMask functions.
If the overlapped operation cannot be completed immediately, the function returns FALSE and the GetLastError function returns ERROR_IO_PENDING, indicating that the operation is executing in the background. When this happens, the system sets the hEvent member of the OVERLAPPED structure to the not-signaled state before WaitCommEvent returns, and then it sets it to the signaled state when one of the specified events or an error occurs. The calling process can use one of the wait functions to determine the event object's state and then use the GetOverlappedResult function to determine the results of the WaitCommEvent operation. GetOverlappedResult reports the success or failure of the operation, and the variable pointed to by the lpEvtMask parameter is set to indicate the event that occurred.
If a process attempts to change the device handle's event mask by using the SetCommMask function while an overlapped WaitCommEvent operation is in progress, WaitCommEvent returns immediately. The variable pointed to by the lpEvtMask parameter is set to zero.
Windows CE: Windows CE supports an additional flag for the lpEvtMask parameter:
The WaitCommEvent function cannot be performed as an overlapped operation. The lpOverlapped parameter is not supported and is ignored. It should be set to NULL before calling WaitCommEvent.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winbase.h.
Import Library: Use kernel32.lib.
Communications Overview, Communication Functions, CreateFile, DCB, GetCommMask, GetOverlappedResult, OVERLAPPED, SetCommMask, SetCommState