Qt creator c++11 only works with main.cpp

(sorry for my english)

I am working with qt creator, My problem is that when I use c++11 in qt, it only works in the main.cpp code and not in other clases, the others cpp clases are compiled without c++11 (I think in c++0xx).

Details: I start a console application and in the .pro file I put the "CONFIG += c++11" thinking that is all that is needed to compile all cpp clases with c++11.

PROBLEM: If I use, for instance, "std::to_string()" in main.cpp I have no problem, but if I create a new Cpp class (with qt creator IDE) and I put "to_string()" in the class then I have a error that says that I have to use c++11.

I hope that you know how to fix my problem.

Regards!