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

Found 10 testcases.