Compilare: user.cpp: In member function ‘bool cmp::operator()(std::tuple<int, int, int>, std::tuple<int, int, int>)’: user.cpp:14:72: warning: control reaches end of non-void function [-Wreturn-type] if( get<2>(t1) != get<2>(t2) ) return get<2>(t1) < get<2>(t2); } }; ^