$ cat set.cpp
   #include <unordered_set>
   #include <iostream>

   int main() {
   char c;
   std::unordered_set<char *> x;
   x.insert(&c);
   std::cout << x.size() << "\n";
   }

   $ clang++ -stdlib=libc++ set.cpp -o sss -g && lldb ./sss -o "b main" -o r -b -o "n" -o n -o "p x"
   [...]
   (lldb) n
   Process 585854 stopped
   * thread #1, name = 'sss', stop reason = step over
      frame #0: 0x0000555555555318 sss`main at set.cpp:8:18
      5   	  char c;
      6   	  std::unordered_set<char *> x;
      7   	  x.insert(&c);
   -> 8   	  std::cout << x.size() << "\n";
      9   	}
   (lldb) p x
   (std::unordered_set<char *>) size=1 {
   [0] = 0x00007fffffffea1f ""
   }

   $ clang++  set.cpp -o sss -g && lldb ./sss -o "b main" -o r -b -o "n" -o n -o "p x"
   [...]
   (lldb) n
   Process 585870 stopped
   * thread #1, name = 'sss', stop reason = step over
      frame #0: 0x000055555555524e sss`main at set.cpp:8:18
      5   	  char c;
      6   	  std::unordered_set<char *> x;
      7   	  x.insert(&c);
   -> 8   	  std::cout << x.size() << "\n";
      9   	}
   (lldb) p x
   (std::unordered_set<char *>) size=0 {}