title: How to #include existing header files in Qt?
body: <p>I have some previously written headers and I would like to include them in my Qt project. How can I do that without copying them in place? </p>
  
  <p>After I added them with "Add Existing Files..." I can't seem to be able to #include my headers. Neither #include "header.h" nor #include "fullpath/header.h" works.</p>