What does CONFIG += x11 actually do?
Simple Question, what does >CONFIG += x11< if defined for qmake?
It is part of the general configuration. However the docs are not very verbose about that:
"The project is an X11 application or library."
If compiling with -Wmissing-include-dirs g++ complains about:
/usr/X11R6/include: No such file or directory [-Werror]
If not using it on Ubuntu14.04 my QtGui-Application seems to run fine. Is my guess correct, that those included are resolved by the QtGui-Library if using it, and I only would need that flag if I would make use of the X11-development files?
I only would need that flag if I would make use of the X11-development files?
Yes. Just ignore it (don't set the config value) for the most of cases.