foo.cc:21:5: error: empty character constant
  bd['':
     ^~
foo.cc: In function 'void init()':
foo.cc:21:7: error: expected ']' before ':' token
  bd['':
       ^
foo.cc:21:7: error: expected ';' before ':' token
foo.cc:21:7: warning: statement has no effect [-Wunused-value]
  bd['':
  ~~~~~^
foo.cc: At global scope:
foo.cc:24:2: error: expected unqualified-id before 'return'
  return 0;
  ^~~~~~
foo.cc:25:1: error: expected declaration before '}' token
 }
 ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。