title: std::vector of std::vectors contiguity
body: <p>I know that <code>std::vector&lt;T&gt;</code> internally stores it's data contiguously (unless it is <code>std::vector&lt;bool&gt;</code>) both in the old <code>C++03</code> standard and the new <code>C++11</code>.</p>
  
  <p>Nice stackoverflow questions that deal with this and quote the standard: <a href="https://stackoverflow.com/a/849190/884412">answer</a>, <a href="https://stackoverflow.com/a/247764/884412">answer</a>.</p>
  
  <p>What about the data inside nested vectors <code>std::vector &lt;std::vector &lt;T&gt; &gt;</code>? How is that stored?</p>
  
  <p>If every internal vector needs to store it's data contiguously, how can it be true that <code>&amp;v[n] == &amp;v[0] + n for all 0 &lt;= n &lt; v.size()</code>.</p>
  
  <p>To phrase this slightly different, is it possible to access <em>all the elements</em> stored in such nested structure "simply" and sequentially (via a pointer or similar) the same way it can be done for a 1-D vector?</p>