title: Error : 'QtGui/QMainWindow': No such file or directory : Qt 5.1.1
body: <p>I have installed the <code>Qt5.1.1</code> and create a new Gui Application. The code in mainwindow.h shows:</p>
  
  <pre><code>#if QT_VERSION &gt;= 0x050000
  #include &lt;QtWidgets/QMainWindow&gt;
  #else
  #include &lt;QtGui/QMainWindow&gt;
  #endif
  </code></pre>
  
  <p>I think it is fine. But when I run it, I have this:</p>
  
  <pre><code>error: C1083: Cannot open include file: 'QtGui/QMainWindow': No such file or directory
  </code></pre>
  
  <p>I know when I replace </p>
  
  <pre><code>#if QT_VERSION &gt;= 0x050000
  #include &lt;QtWidgets/QMainWindow&gt;
  #else
  #include &lt;QtGui/QMainWindow&gt;
  #endif
  </code></pre>
  
  <p>to</p>
  
  <pre><code>#include &lt;QtWidgets/QMainWindow&gt;
  </code></pre>
  
  <p>it works.</p>
  
  <p>I just wonder why the default code is wrong and how to make the defauly code right.</p>