title: C++ possible to overload `operator<<` to display map?
body: <p>I overloaded my <code>operator&lt;&lt;</code> as the following:</p>
  
  <pre><code>friend ostream&amp; operator&lt;&lt;(ostream&amp; os, Data&amp; e)
  {
      // possible code for printing map..
      return os;
  }
  </code></pre>
  
  <p>And I have a <code>map&lt;string, vector&lt;int&gt;&gt; table</code>, my question is, is it possible to access and print out the map through <code>e.table</code>?</p>