title: How can I display results of a timer with a putText in C++ OpenCV?
body: <p>How can I display results od a timer with a putText in my OpenCV Android app? The is detecting features on the view from a camera and the main algorithm and the timer is written in C++. The full code of my C++ JNI file:</p>
  
  <pre><code>#include &lt;jni.h&gt;
  #include &lt;opencv2/core/core.hpp&gt;
  #include &lt;opencv2/imgproc/imgproc.hpp&gt;
  #include &lt;opencv2/features2d/features2d.hpp&gt;
  #include &lt;vector&gt;
  
  using namespace std; 
  using namespace cv;
  
  extern "C" {
  JNIEXPORT void JNICALL  
  Java_org_opencv_samples_tutorial3_Sample3View_FindFeatures(JNIEnv* env, jobject, jint 
  width, jint height, jbyteArray yuv, jintArray bgra)   
  {
  jbyte* _yuv  = env-&gt;GetByteArrayElements(yuv, 0);
  jint*  _bgra = env-&gt;GetIntArrayElements(bgra, 0);
  
  Mat myuv(height + height/2, width, CV_8UC1, (unsigned char *)_yuv);
  Mat mbgra(height, width, CV_8UC4, (unsigned char *)_bgra);
  Mat mgray(height, width, CV_8UC1, (unsigned char *)_yuv);
  
  //Please make attention about BGRA byte order
  //ARGB stored in java as int array becomes BGRA at native level
  cvtColor(myuv, mbgra, CV_YUV420sp2BGR, 4);
  
  vector&lt;KeyPoint&gt; v;
  
  OrbFeatureDetector  detector(1);
  double t = (double)getTickCount();
  detector.detect(mgray, v);
  t = ((double)getTickCount() - t)/getTickFrequency();
  putText(mbgra, t+" detection time", Point2f(100,100), FONT_HERSHEY_PLAIN, 2, Scalar(0,0,255,255), 2);
  for( size_t i = 0; i &lt; v.size(); i++ )
      circle(mbgra, Point(v[i].pt.x, v[i].pt.y), 10, Scalar(0,0,255,255));
  env-&gt;ReleaseIntArrayElements(bgra, _bgra, 0);
  env-&gt;ReleaseByteArrayElements(yuv, _yuv, 0); }}
  </code></pre>
  
  <p>The problem is in the line with putText: I get an error "invalid operands of types 'double' and 'char const [15]' to binary 'operator+'". Is my timer OK? How else can I display the results of it? I will be grateful for your help.   </p>