title: Boost spirit debug output does not appear
body: <p>I am trying the Second Answer of <a href="https://stackoverflow.com/questions/17012941/boostspirit-how-to-parse-and-call-c-function-like-expressions">this question</a>. The parsing itself works fine, but after uncommenting the <code>#define BOOST_SPIRIT_DEBUG</code> on the first line, the <code>BOOST_SPIRIT_DEBUG</code> output still does not appear anywhere.</p>
  <p>When I add these 3 lines below to the <code>main()</code>, I am seeing all 3 lines appear in my terminal. However, I don't see any parser debug lines. What is missing?</p>
  <pre><code>std::cout &lt;&lt; &quot;Hello cout&quot; &lt;&lt; std::endl;
  std::cerr &lt;&lt; &quot;Hello cerr&quot; &lt;&lt; std::endl;
  BOOST_SPIRIT_DEBUG_OUT &lt;&lt; &quot;Hello boost spirit debug out&quot; &lt;&lt; std::endl;
  </code></pre>
  <p>Probably worth mentioning I am using Qt Creator.</p>