title: Why does std::distance doesn't work on iterator of unordered_map?
body: <p>I have this code:</p>
  <pre><code>#include &lt;bits/stdc++.h&gt;
  #include &lt;iostream&gt;
  using namespace std;
  
  int main()
  {
      unordered_map&lt;int, int&gt; umap;
      unordered_map&lt;int, int&gt;::iterator itr1, itr2;
      itr1 = umap.begin();
      itr2 = std::next(itr1, 3);
      cout &lt;&lt; distance(itr2, itr1);
      return 0;
  }
  </code></pre>
  <p>It compiles fine. But produces a <code>Segmentation fault</code> upon executing.</p>
  <p>Why can't I find the distance between iterators?</p>