foo.cc: In function 'int main()':
foo.cc:10:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("unhappy.in","r",stdin);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:11:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("unhappy.out","w",stdout);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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