Monitoring Communications Events

The following example code opens the serial port for overlapped I/O, creates an event mask to monitor CTS and DSR signals, and then waits for an event to occur. The WaitCommEvent function should be executed as an overlapped operation so the other threads of the process cannot perform I/O operations during the wait.

HANDLE hCom;
OVERLAPPED o;
BOOL fSuccess;
DWORD dwEvtMask;

hCom = CreateFile( "COM1",
    GENERIC_READ | GENERIC_WRITE,
    0,    // exclusive access 
    NULL, // no security attributes 
    OPEN_EXISTING,
    FILE_FLAG_OVERLAPPED,
    NULL
    );

if (hCom == INVALID_HANDLE_VALUE) 
{
    // Handle the error. 
}

// Set the event mask. 

fSuccess = SetCommMask(hCom, EV_CTS | EV_DSR);

if (!fSuccess) 
{
    // Handle the error. 
}

// Create an event object for use in WaitCommEvent. 

o.hEvent = CreateEvent(
    NULL,   // no security attributes 
    FALSE,  // auto reset event 
    FALSE,  // not signaled 
    NULL    // no name 
    );

assert(o.hEvent);

if (WaitCommEvent(hCom, &dwEvtMask, &o)) 
{
    if (dwEvtMask & EV_DSR) 
    {
         // To do.
    }

    if (dwEvtMask & EV_CTS) 
    {
         // To do. 
    }
}