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. 
    }
}