title: Another "No such file or directory" error in qt5
body: <p>So, I encounter another interesting "no such file or directory" error in my program.</p>
  
  <p>The interesting thing is, when I typed the classes I include in my source code, which are <strong>QGraphicsItem</strong> and <strong>QGraphicsView</strong> in this case, no warning was given. But when I tried to built it in Qt creator, it raise an error and told me that <strong>"C1083: can not open include file:No such file or directory"</strong>.  (The header file both locate at  <strong>D:\Qt\Qt5.4.1\5.4\msvc2013_64\include\QtWidgets</strong>)</p>
  
  <p>Also, I went check the include path in my qt5.4 file, which is <strong>D:\Qt\Qt5.4.1\5.4\msvc2013_64\include</strong> in his case, I did exactly find the two header files.</p>
  
  <p>Has any one met this error before? Can explain it?</p>
  
  <p>And by the way, which is the default include path in qt creator and how to change it?</p>