title: Adding unnamed nodes to boost::property_tree::ptree
body: <p>I need to add unnamed nodes to a boost::property_tree::ptree just like it's JSON parser does for arrays. However when I want to do it I get such assertion during runtime:</p>
  
  <pre><code>  Assertion failed: !p.empty() &amp;&amp; "Empty path not allowed for put_child.", file C:\Program Files\Boost\boost\include/boost/property_tree/detail/ptree_implementation.hpp, line 877
  </code></pre>
  
  <p>I do it like</p>
  
  <pre><code>tree.add_child(name, child);
  </code></pre>
  
  <p>where tree and child are both ptree-s and name char*.</p>
  
  <p>How could I do it like the JSON parser for ptree-s does?</p>