/in/foo.cc:55:5: error: 'int clock' redeclared as different kind of entity
   55 | int clock;
      |     ^~~~~
In file included from /usr/include/pthread.h:23,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/gthr-default.h:35,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/gthr.h:148,
                 from /usr/include/c++/12/ext/atomicity.h:35,
                 from /usr/include/c++/12/bits/ios_base.h:39,
                 from /usr/include/c++/12/ios:42,
                 from /usr/include/c++/12/ostream:38,
                 from /usr/include/c++/12/iostream:39,
                 from /in/foo.cc:45:
/usr/include/time.h:72:16: note: previous declaration 'clock_t clock()'
   72 | extern clock_t clock (void) __THROW;
      |                ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:75:11: error: assignment of function 'clock_t clock()'
   75 |     clock = n;//时间戳
      |     ~~~~~~^~~
/in/foo.cc:81:17: warning: ISO C++ forbids decrementing a pointer of type 'clock_t (*)() noexcept' {aka 'long int (*)()'} [-Wpointer-arith]
   81 |         id[u] = clock--;
      |                 ^~~~~
/in/foo.cc:81:17: error: lvalue required as decrement operand