It looks like the Makefile was not regenerated when you edited the .pro file.
Run qmake and try again.
You could also check if the deck.cpp is compiled or not; is there a deck.o in the build directory ?
It looks like the Makefile was not regenerated when you edited the .pro file.
Run qmake and try again.
You could also check if the deck.cpp is compiled or not; is there a deck.o in the build directory ?