title: How can I determine if a dialog is null in Qt?
body: <p>I'm trying to show a simple dialog like this:</p>
  
  <pre><code>if (!aboutDialog)
          aboutDialog = new AboutDialog(this);
      aboutDialog-&gt;exec();
  </code></pre>
  
  <p>For some reason it doesn't work (aboutDialog has some pointer although is not initialized), the checking <code>if (aboutDialog == 0)</code> doesn't work either. I don't want to create the instance every time, but only once. How do I check this properly?</p>
  
  <p>Thanks!</p>