Qt creator Adding external library (still: Cannot open include file: 'GL/glew.h')

Question

I followed the instruction:

1. In the Projects pane, open the project file (.pro).
2. Right-click in the code editor to open the context menu and select Add

Answer 1

I had the same problem and I figured it out just now: You have to run qmake(build->run qmake) to validate changes in the pro file.