title: Access to specific index in ptree array
body: <p>I am using boost library to manipulate a JSON file and I would like to access to a specific index of an array in this JSON.</p>
  
  <pre><code>boost::property_tree::ptree&amp; jsonfile;
  const boost::property_tree::ptree&amp; array =
    jsonfile.get_child("my_array");
  </code></pre>
  
  <p>What I would like to do is accessing to the value stored at index :</p>
  
  <pre><code>// This code does not compile
  int value = array[index].get &lt; int &gt; ("property");
  </code></pre>