title: Qt error: 'const class QString' has no member named 'toStdString'
body: <p>I am getting this error <code>error: 'const class QString' has no member named 'toStdString'</code> though <code>QString</code> has it. <a href="http://qt-project.org/doc/qt-4.8/qstring.html#toStdString" rel="noreferrer">(link)</a>. </p>
  
  <p>The code</p>
  
  <pre><code>    std::string Message::toStdString() const 
      {
          return m_string.toStdString();
      }
  </code></pre>