title: How to understand function ostream& operator<< (ostream& os, const unsigned char* s)
body: <p>For function declaration like</p>
  
  <pre><code>ostream&amp; operator&lt;&lt; (ostream&amp; os, const unsigned char* s);
  </code></pre>
  
  <p>I am wondering what has been returned. The CPP reference says it returns ostream object. But why it is ostream&amp; instead of simple ostream?</p>
  
  <p>Thank you</p>