title: C++: string operator overload
body: <p>Can I overload existing function/operator in existing class?</p>
  
  <p>I was trying to do:</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;string&gt;
  using namespace std;
  
  string&amp; string::operator&lt;&lt;(const string&amp; str) {
    this-&gt;append(str);
  }
  </code></pre>
  
  <p>But this gives me error:</p>
  
  <pre><code>test.cpp:5: error: too few template-parameter-lists
  </code></pre>
  
  <p>How can I do this? Or I can't?</p>