foo.cc: In function 'int main()':
foo.cc:6:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("rabbit.in","r",stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
foo.cc:7:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("rabbit.out","w",stdout);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。