Error in BackgroundSubtraction Mog2

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I am using opencv 2.4.4 and when i run this algorithm on it , it give me the error on nmixtures and bShadowDetection

    cv::VideoCapture cap("try2.avi");
    cv::BackgroundSubtractorMOG2 bg;
    bg.nmixtures = 3;
    bg.bShadowDetection = false;
//When i use it like below , it didn't give syntax error , but give me error at runtime bg.set("nmixtures", 3); bg.set("bShadowDetection", false);

    std::vector<std::vector<cv::Point> > contours;

    cv::namedWindow("Frame");
    cv::namedWindow("Background");

    for(;;)
    {
        cap >> frame;
        bg.operator ()(frame,fore);
        bg.getBackgroundImage(back);
        cv::erode(fore,fore,cv::Mat());
        cv::dilate(fore,fore,cv::Mat());
        cv::findContours(fore,contours,CV_RETR_EXTERNAL,CV_CHAIN_APPROX_NONE);
        cv::drawContours(frame,contours,-1,cv::Scalar(0,0,255),2);
        cv::imshow("Frame",frame);
        cv::imshow("Background",back);
        if(cv::waitKey(30) >= 0) break;
    }

Error's

error C2248: 'cv::BackgroundSubtractorMOG2::nmixtures' : cannot access protected member declared in class 'cv::BackgroundSubtractorMOG2'
`error C2248: 'cv::BackgroundSubtractorMOG2::bShadowDetection' : cannot access protected member declared in class 'cv::BackgroundSubtractorMOG2`'   

    error LNK2019: unresolved external symbol "public: virtual void __thiscall cv::BackgroundSubtractorMOG2::operator()(class cv::_InputArray const &,class cv::_OutputArray const &,double)" (??RBackgroundSubtractorMOG2@cv@@UAEXABV_InputArray@1@ABV_OutputArray@1@N@Z) referenced in function _main