title: Reverse iterating with 2 loops?
body: <p>Basically I want to reverse iterate through 2 std::vectors.
  a layer has a vector of shapes.</p>
  
  <p>usually I could do something like this:</p>
  
  <pre><code>for(int i = 0; i &lt; layers.size(); ++i)
  {
     for(int j = 0; j &lt; layers[i].shapes.size(); ++j)
     {
        layers[i].shapes[j].dosomething();
     }
  }
  </code></pre>
  
  <p>However right now I need to reverse iterate through the vectors and therefore need to use a reverse iterator but how would this work? Since iterators kind of make it like a for each, how can I acces the current shape of the current layer being iterated through?
  Thanks</p>