c -如何克服lex文件中未声明的错误

Question

我是lex的新手，我在文件ilk.l中编写了非常简单的程序

%option main
%%
float val;
[+-]?[0-9]*(.)?[0-9]+      {sscanf(yytext, "%f", &val);
printf(">%f<", val);     }

保存该文件后，运行以下命令:

-bash-4.2$ lex ilk.l
-bash-4.2$ gcc lex.yy.c
ilk.l: In function ‘yylex’:
ilk.l:3:1: error: ‘val’ undeclared (first use in this function)
float val;
^
ilk.l:3:1: note: each undeclared identifier is reported only once for each function it appears in
-bash-4.2$

我对错误的原因感到困惑。你能解释一下我做错了什么，我该如何改正吗?

Answer 1

变量应该在声明部分如下声明:

%{
//declaration section
float val;
%}
%option main
%%
[+-]?[0-9]*(.)?[0-9]+ {sscanf(yytext, "%f", &val);printf(">%f<", val);}
%%