title: Using boost property tree to read int array
body: <p>I have some JSON with a handful of integer array variables, like so:</p>
  
  <pre><code>{"a": [8, 6, 2], "b": [2, 2, 1]}
  </code></pre>
  
  <p>I would like to use boost property_tree, for instance:</p>
  
  <pre><code>std::stringstream ss;
  boost::property_tree::ptree pt;
  
  ss &lt;&lt; "{\"a\": [8, 6, 2], \"b\": [2, 2, 1]}";
  
  boost::property_tree::read_json(ss, pt);
  std::vector&lt;int&gt; a = pt.get&lt;std::vector&lt;int&gt; &gt;("a");
  </code></pre>
  
  <p>This doesn't work, nor does any variation on an int pointer that I've tried. How may I read an array from a property tree?</p>