With a 15 pages that the search of the forum returned, I finally found topic that answer to my question:
http://www.qtcentre.org/forum/f-qt-p...ation-631.html

The other question is even if I pass the pointer of qApp to the DLL from the interface, how I will be able to set correct pointer to QApplication::instance(), I can't find a set method, tomorow I will try some things... If anyone have an idea in the mean time, please let me know.