consider that i have a main.cpp file in root which include "mainview.h" in it.
The mainview.h file is in root/View.
I have configured the .pro file(add View/mainview.h to HEADERS tag) but it still can't find mainview header in main.cpp
If you do e.g.
then the preprocessor will look first in the same directory as the source file doing the
#include, then it will look in the system directories. If you have a header file in a sub-directory then you need to specify that too: