So... after isntalling gcc4.7, I found I had gcc4.5, 4.6 and 4.7. After configuring alternatives, when typing gcc --version it said it was 4.7, but I was not sure that Qtcreator were using the right one, so I decided to erase 4.5 and 4.6.
And... I shouldn't have done that. Now, even when I reinstalled 4.6 with aptitude, gcc command is not found (/usr/bin/gcc: NO such file or directoy).
I need to fix this or I can't continue working. I'm only interested in having 4.7. Any help?