facerecognizer save() method

edit

I miss a problem when I using the save() method in my face recognizer project. My code is:

    Ptr<FaceRecognizer> model = createEigenFaceRecognizer();
model->set("threshold",100.0);
model->train(images,labels);
model->save("/sdcard/Train_model.xml");

I can't open the file /sdcard/Train_model.xml in my project. I want to know whether the save method can create a new file. I hope that I can get your help,thanks My error is