$ make
/usr/bin/uic-qt4 principal.ui -o ui_principal.h
g++  -o retrovisa     -L/usr/lib -lQtGui -lQtCore -lpthread
/usr/lib/gcc/i486-linux-gnu/4.1.2/../../../../lib/crt1.o: In function `_start':
../sysdeps/i386/elf/start.S:115: undefined reference to `main'
collect2: ld returned 1 exit status
make: ** [retrovisa] Erro 1