How to get svm predict scores?

edit

image read:

Mat image = imread(buffer, IMREAD_GRAYSCALE);

predict:

SVM->predict(imgDescriptor, testResponse,cv::ml::SVM::UPDATE_MODEL);
cout << "rows: " << testResponse.rows << endl;
cout << "cols: " << testResponse.cols << endl;
cout << "res: " << res << endl;

out put:

rows: 1
cols: 1
res: 0

How to get svm predict socres?