%{#include <stdio.h>#include <stdlib.h>int num_num = 0;int num_id = 0;
%}
INTEGER [-+]?[1-9][0-9]*
ID [a-zA-Z][a-zA-Z_0-9]*
SPACE [ \n\t]
%%
{INTEGER} { num_num++;printf("(num = %d)\n", atoi(yytext));/*打印数字值*//*数字数加一*/
}{ID} { num_id++;printf("(id = %s)\n", yytext);
}{SPACE} |
. {/*什么也不做,滤掉白字符和其它字符*/
}
%%int main()
{yylex();printf("num = %d, id = %d\n", num_num, num_id);return 0;
}int yywrap()//此函数必须由用户提供,或者声明 %option noyywrap
{return 1;
}

编译运行：

$ flex lex.l$ gcc lex.yy.c -o lex.out$ ./lex.out
aaa bbb abc 239(id = aaa)
(id = bbb)
(id = abc)
(num = 239)
num = 1, id = 3