foo.cc: In function 'int main()':
foo.cc:43:29: warning: 'f2' may be used uninitialized in this function [-Wmaybe-uninitialized]
     std::cout<<f1<<" "<<f2<<"\n";
                             ^~~~
foo.cc:43:20: warning: 'f1' may be used uninitialized in this function [-Wmaybe-uninitialized]
     std::cout<<f1<<" "<<f2<<"\n";
                    ^~~