title: issue with ostream and << overloading
body: <p>I have this printing line of code:</p>
  
  <pre><code> std::cout &lt;&lt; *it &lt;&lt; std::endl;
  </code></pre>
  
  <p>now, since 'it' is a complex type I need to write my own '&lt;&lt;' operator.
  this is my function:</p>
  
  <pre><code>friend ostream&amp; operator&lt;&lt;(ostream&amp; os, const Node&amp; n ){
      return os &lt;&lt; n.key &lt;&lt; ':' &lt;&lt; n.value;
  }
  </code></pre>
  
  <p>I get an error "type ostream could not be resolved"
  I've tried adding std:: before "ostream" but that doesn't help. I'm not sure what else I can try. </p>