foo.cc: In member function 'void LinkStack::Match(char*)':
foo.cc:61:11: warning: unused variable 't' [-Wunused-variable]
   61 |      char t = pop();//出栈
      |           ^
foo.cc:37:9: warning: variable 'L' set but not used [-Wunused-but-set-variable]
   37 |    char L = '\0';//左括号
      |         ^
foo.cc:80:12: warning: unused variable 'a' [-Wunused-variable]
   80 |    if (int a = empty() == true)
      |            ^

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