$ qmake -project && qmake -spec macx-g++ && make
Makefile:224: warning: overriding commands for target `main.o'
Makefile:221: warning: ignoring old commands for target `main.o'
c++ -headerpad_max_install_names -o t5.app/Contents/MacOS/t5 main.o main.o -F/Library/Frameworks -L/Library/Frameworks -framework QtGui -framework Carbon -framework AppKit -framework QtCore -lz -lm -liconv -framework ApplicationServices
/usr/bin/ld: multiple definitions of symbol MyWidget::MyWidget(QWidget*)
main.o definition of MyWidget::MyWidget(QWidget*)in section (__TEXT,__text)
main.o definition of MyWidget::MyWidget(QWidget*)in section (__TEXT,__text)
/usr/bin/ld: multiple definitions of symbol MyWidget::MyWidget(QWidget*)
main.o definition of MyWidget::MyWidget(QWidget*)in section (__TEXT,__text)
main.o definition of MyWidget::MyWidget(QWidget*)in section (__TEXT,__text)
/usr/bin/ld: multiple definitions of symbol _main
main.o definition of _main in section (__TEXT,__text)
main.o definition of _main in section (__TEXT,__text)
collect2: ld returned 1 exit status
make: *** [t5.app/Contents/MacOS/t5] Error 1