/in/foo.c:1:30: warning: '-std=c++11' is not an option that controls warnings [-Wpragmas]
 #pragma GCC diagnostic error "-std=c++11"  //如果你用了stl，这段最好别加
                              ^~~~~~~~~~~~
/in/foo.c:51:20: fatal error: iostream: No such file or directory
 #include <iostream>
                    ^
compilation terminated.