In file included from iostream:39:
In member function 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>]',
    inlined from 'int main()' at foo.cc:20:10:
/nix/store/1x1q5sqa0ilbi8fz7aayk02pjy5g7jhh-gcc-12.3.0/include/c++/12.3.0/ostream:206:25: warning: 'xB' may be used uninitialized [-Wmaybe-uninitialized]
  206 |       { return _M_insert(__n); }
      |                ~~~~~~~~~^~~~~
foo.cc: In function 'int main()':
foo.cc:10:23: note: 'xB' was declared here
   10 |    unsigned long long xB;
      |                       ^~

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