lex不在MAC OS X上工作

Question

  "_main", referenced from:
      start in crt1.10.6.o
  "_yywrap", referenced from:
      _yylex in ccY7a1Un.o
      _input in ccY7a1Un.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

这是我以%%的形式运行一个简单的lex程序时得到的错误。在其他地方，同样的程序运行正常。