/in/foo.cc: In function 'void link(int, int)':
/in/foo.cc:58:2: error: reference to 'rank' is ambiguous
  rank[tid[u]] = u;
  ^~~~
/in/foo.cc:26:5: note: candidates are: int rank [100000]
 int rank[maxn], son[maxn], pos, val[maxn], n, q;
     ^~~~
In file included from /usr/include/c++/6/bits/move.h:57:0,
                 from /usr/include/c++/6/bits/nested_exception.h:40,
                 from /usr/include/c++/6/exception:173,
                 from /usr/include/c++/6/ios:39,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/type_traits:1482:12: note:                 template<class> struct std::rank
     struct rank
            ^~~~