How we can use dlib's image data (parts & rect points) from c++ to c# using PInvoke method?

Question

I am using Dlib - Face_detection_landmark.cpp in my c++ project.

my .cpp code as below :

__declspec(dllexport) char* FaceDetection( const wchar_t* filename)
{
    std::wstring ws(filename);
    String path(ws.begin(), ws.end());
    array2d<unsigned char> img;
    load_image(img, path);
    pyramid_up(img);
     
    frontal_face_detector detector = get_frontal_face_detector();

    // Now tell the face detector to give us a list of bounding boxes
    // around all the faces it can find in the image.
    std::vector<dlib::rectangle> dets = detector(img);
    std::string imageRect = "" + std::to_string(dets[0].left()) + 
                                  std::to_string(dets[0].left());

    char* pchr = (char*)imageRect.c_str();
    return pchr;
 }
}

And my c# code is :

[DllImport("FaceDetector.dll", 
           CallingConvention = CallingConvention.Cdecl, 
           CharSet = CharSet.Unicode)]
static extern string FaceDetection(string filename);

void main()
{
     string filename = "some path";
     string s = "";
     s = FaceDetection(filename);
}
     

Error : value of string s is null.

Anyone can help on this?

Answer 1

等待大神答复