I found the problem. The problem is that i'm using qtdesigner 4.2.4. But this application, since it's not the commercial, can't generate the cpp code has qtdesigner 3.3.7.
1 - Is it true that qtdesigner 4.2.4 for linux can't create cpp code, because i've installed the free version, and not the commercial?
2 - If so, personally, i don't understand why. If the qtdesigner 3.3.7 can generate cpp code, and 4.2.4 can't, probably, few people that use qtdesign at home (like me) will stick to the version 3.3.7. That's toobad.