title: std::unordered_map initialization
body: <p>When I access an element in <a href="http://en.cppreference.com/w/cpp/container/unordered_map/operator_at" rel="noreferrer">std::unordered_map using operator []</a> for the first time, it is automatically created. What (if any) are guarantees about its initialization? (It is guaranteed to be value initialized, or only to be constructed)?</p>
  
  <p>Example:</p>
  
  <pre><code>std::unordered_map&lt;void *, size_t&gt; size;
  char *test = new char[10];
  size[test] += 10;
  </code></pre>
  
  <p>Is size[test] guaranteed to be 10 at the end of this sequence?</p>