using timer in serial communication causes unhandled exception

[bruffchewren]

I am coding in c++ mfc where i try to do serial communication.
I have successfully done all the connection to the camera and even receive data from the camera.

However, ran into some problems.

When i was running the program however, i got a "Unhandled exception at 0x7833dcfa (mfc80ud.dll) in SerialCommunication.exe: 0xC0000005: Access violation reading location 0x00000020"

It points to this particular line.
SetTimer(1, 100,NULL);

the timer is being used in a way such that it will be set when it is trying to receive/send data from the camera through a serial communication and if data is not received within tat timer period, the program will abort the operation.

[Banfa]

Post the actual code, are you sure the window object you are calling it through is valid? An invalid this pointer could cause such an error but it is not likely the SetTimer call itself is causing it.

[weaknessforcats]

According to MSDN, the first argument for SetTimer is an hWnd which is either NULL or is a valid handle to a window owned by the current thread.

Why is your first argument a 1?

[Banfa]

I think because MFC is being used, that SetTimer call has exactly 1 parameter less than required which corresponds to the SetTimer method of the CWnd class. And is the reason I requested the actual code.

[weaknessforcats]

It may be some obj->SetTimer where obj is a CWnd*, but I just took the post at face value. I have to watch out doing that.

[bruffchewren]

sorry for the late reply people.

This is the code for connecting to the port

bool CSerialControl::Connect(CString portName, CString btnName)
{
 
   // fill timeout structure
    GetCommTimeouts(hComm, &timeout);
    timeout.ReadIntervalTimeout = 100;          
    timeout.ReadTotalTimeoutConstant = 100;
    timeout.ReadTotalTimeoutMultiplier = 0;
    timeout.WriteTotalTimeoutConstant = 100;
    timeout.WriteTotalTimeoutMultiplier = 100;    
 
    SetCommTimeouts(hComm, &timeout);
 
    portName = _T("\\\\.\\") + portName;
    hComm = CreateFile( portName, GENERIC_READ |  GENERIC_WRITE, 0, NULL, OPEN_EXISTING,  0, NULL ) ;
    if( hComm == INVALID_HANDLE_VALUE )
    {
        AfxMessageBox( _T( "Error opening Port" ) ) ;
        return false;
    }
    else
        return true;
 
}

This is the method which calls the settimer
Note 1 : uResult is UINT declared globally.
Note 2: Global variable const UINT ID_TIMER = 0x1001;

/*method to read camera replies */
bool CSerialControl::ReadCameraParameter()
{
    char m_ReceiveBuffer[ 5000 ] ;
    DWORD m_CharRead ;
 
    m_CharRead = NULL ;
 
 
 
    uResult = SetTimer( ID_TIMER ,100,NULL);
    ReadFile( hComm, m_ReceiveBuffer, 5000, &m_CharRead, NULL ) ;
 
 
    if ( uResult == 0 )
    {
        AfxMessageBox(_T("Error: Could not connect the RS232 port!"), MB_OK|MB_ICONEXCLAMATION);
        // Stop the timer. Indirectly it will stop the reading
        BOOL blStatus = KillTimer(uResult) ;
 
        // Check Whether the timer is killed properly or not.
        if ( blStatus == 0 )
            AfxMessageBox(_T("Error: Could not stop the watching of RS232 port!"),  MB_OK|MB_ICONEXCLAMATION);
 
        // Reset the handle variable
        CloseHandle( hComm) ;
        return false;
    }     
    if( m_CharRead == NULL ) 
        return false ;
 
    ci.camName = GetParam(m_ReceiveBuffer, "Camera Model No.:");
    ci.serial = GetParam(m_ReceiveBuffer, "Camera Serial No.:" );
    ci.firmware = GetParam(m_ReceiveBuffer, "Firmware Design Rev.:" );
    ci.cci = GetParam(m_ReceiveBuffer, "CCI Version:");
    ci.fgpa = GetParam(m_ReceiveBuffer, "FPGA Version:");
    ci.exposure = GetParam(m_ReceiveBuffer, "Exposure Mode:");
    ci.baudrate = GetParam(m_ReceiveBuffer, "UART Baud Rate:");
    ci.tdi = GetParam(m_ReceiveBuffer, "TDI Mode:");
    ci.mirror = GetParam(m_ReceiveBuffer, "Mirroring Mode:");
 
 
 
 
    return true;
}
 

and finally, the ontimer handler method

void CSerialControl::OnTimer(UINT_PTR nIDEvent)
{
 
                if( nIDEvent == ID_TIMER )
                      uResult --;
    CDialog::OnTimer(nIDEvent);
}
 

I was thinking it was the handler to the settimer too!but i cant seem to find whats wrong with it :(