title: How to retrieve the key-value pairs from an OpenCV FileNode map?
body: <p>I am storing a map in a yaml file with OpenCV FileStorage, something like this:</p>
  
  <pre class="lang-c prettyprint-override"><code>cv::FileStorage fs("file.yaml.gz", cv::FileStorage::WRITE);
  std::string somekey = ...;
  double someval = ...;
  fs &lt;&lt; "mymap" &lt;&lt; "{:" &lt;&lt; somekey &lt;&lt; someval &lt;&lt; "}";
  </code></pre>
  
  <p>Now, I want to get the data back, but I do not know the keys of the map. I guess the code should be like this:</p>
  
  <pre class="lang-c prettyprint-override"><code>cv::FileStorage fs("file.yaml.gz", cv::FileStorage::READ);
  cv::FileNode fn = fs["mymap"];
  // fn has type == cv::FileNode::MAP
  // fn has size == 1 element (one pair)
  // fn[0] returns also a MAP with 1 element
  </code></pre>
  
  <p>Is is possible to get all the pairs of that map without the keys? I have checked the <code>cv::FileNodeIterator</code>, but it does not seem to solve this problem. The C interface, <code>CvFileNode</code>, allows to retrieve the values but just after providing the key. </p>