WaitCommEvent
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 of
communications device |
|
LPDWORD lpEvtMask, |
// address of
variable for event that occurred |
|
LPOVERLAPPED lpOverlapped, |
// address of
overlapped structure |
|
); |
|
Parameters
hFile
Identifies
the communications device. The CreateFile function returns this handle.
lpEvtMask
Points to a
32-bit variable that receives a mask indicating the type of event that
occurred. If an error occurs, the value is zero; otherwise, it is one of the
following values:
|
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. |
lpOverlapped
Points to an OVERLAPPED structure. This structure
is required if hFile was opened with FILE_FLAG_OVERLAPPED.
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.
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 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 functionsY2TC_3 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.
See Also