title: Iterating vector-based priority_queue
body: <p>I need to iterate over <code>std::vector</code>-based <code>priority_queue</code>. As <a href="https://stackoverflow.com/q/41904374/2052436">many answers</a> here suggest, I can inherit from <code>priority_queue</code> and access underlying container (<code>std::vector</code> in my case).</p>
  <p>Is it guaranteed that <code>priority_queue</code> elements are stored starting from element <code>0</code> of the underlying vector and that vector size equals queue size?</p>
  <p>PS. I am iterating regardless of priority, so I iterate: <code>for (int i = 0; i &lt; c.size(); ++i)</code>...</p>