How to create DPMDetector object inside a class?

I like to use this DPMDetector object inside my class. namespace cv { namespace dpm { /** @brief This is a C++ abstract class, it provides external user API to work with DPM. */ class CV_EXPORTS_W DPMDetector { public: struct CV_EXPORTS_W ObjectDetection { ObjectDetection(); ObjectDetection( const Rect& rect, float score, int classID=-1 ); Rect rect; float score; int classID; }; virtual bool isEmpty() const = 0; /** @brief Find rectangular regions in the given image that are likely to contain objects of loaded classes (models) and corresponding confidence levels. @param image An image. @param objects The detections: rectangulars, scores and class IDs. */ virtual void detect(cv::Mat &image, CV_OUT std::vector<ObjectDetection> &objects) = 0; /** @brief Return the class (model) names that were passed in constructor or method load or extracted from models filenames in those methods. */ virtual std::vector<std::string> const& getClassNames() const = 0; /** @brief Return a count of loaded models (classes). */ virtual size_t getClassCount() const = 0; /** @brief Load the trained models from given .xml files and return cv::Ptr<DPMDetector>. @param filenames A set of filenames storing the trained detectors (models). Each file contains one model. See examples of such files here `/opencv_extra/testdata/cv/dpm/VOC2007_Cascade/`. @param classNames A set of trained models names. If it's empty then the name of each model will be constructed from the name of file containing the model. E.g. the model stored in "/home/user/cat.xml" will get the name "cat". */ static cv::Ptr<DPMDetector> create(std::vector<std::string> const &filenames, std::vector<std::string> const &classNames = std::vector<std::string>()); virtual ~DPMDetector(){} }; } // namespace dpm } // namespace cv I tried like class myClass{ private: DPMDetector *detector;//first approach cv::Ptr<DPMDetector> detector;//second approach public: myClass(); void fun1(void); void fun2(void); } fun1 and fun2 will use detector; If I do like myClass::myClass(){ detector->create(vector<string>(1, "inriaperson.xml"));//first approach detector = DPMDetector::create(vector<string>(1, "inriaperson.xml"));//second approach } For both first and second approaches, I have errors like undefined reference to `cv::dpm::DPMDetector::create(std::vector<std::string, std::allocator<std::string> > const&, std::vector<std::string, std::allocator<std::string> > const&)' How can I create DPMDetector object so that fun1 and fun2 can use?