title: Using .pri files in Qt
body: <p>This is a followup to this question <a href="https://stackoverflow.com/questions/1176666/how-to-create-a-subdirectory-for-a-project-in-qt-creator">How to create a subdirectory for a project in qt-creator?</a>, where the first answer didn't work for me. </p>
  
  <p>I resolved it by manually writing every file into the main .pro file, which is not that much harder, but I still wonder - how exactly .pri files work, and why the solution linked above didn't add the folders, but only the .pri files, so it looked like this in Qt creator:</p>
  
  <p><a href="https://i.stack.imgur.com/80VN6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/80VN6.png" alt="Qt creator screenshot"></a></p>
  
  <p>So, my questions are:</p>
  
  <ul>
  <li>What is the general format of the .pri files?</li>
  <li>Why the solution above doesn't work?</li>
  </ul>