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I started studying jflex. When i try to generate output using jflex for the following code I keep getting an error 

Error in file "\abc.flex" (line 29): 
Unexpected character

[ \t\n]+                ;
^
1 error, 0 warnings.

Generation aborted.

Code trying to run

letter   [a-zA-Z]
digit    [0-9]
intlit      [0-9]+
%{
#include <stdio.h>   
# define BASTYPTOK 257   /*following are output from yacc*/
# define IDTOK 258       /*yacc assigns token numbers */
# define LITTOK 259
# define CINTOK 260
# define INSTREAMTOK 261
# define COUTTOK 262
# define OUTSTREAMTOK 263
# define WHILETOK 264
# define IFTOK 265
# define ADDOPTOK 266
# define MULOPTOK 267
# define RELOPTOK 268
# define NOTTOK 269
# define STRLITTOK 270

main()  /*this replaces the main in the lex library*\
{  int  p;
    while (p= yylex())
              printf("%d is \"%s\"\n", p, yytext);
              /*yytext is where lex stores the lexeme*/}
%}

%%
[ \t\n]+                ;
"//".*"\n"              ;
{intlit}                {return(LITTOK);}
cin                     {return(CINTOK);}
"<<"                    {return(INSTREAMTOK);}
\<|"=="                 {return(RELOPTOK);}
\+|\-|"||"              {return(ADDOPTOK);}
"="                     {return(yytext[0]);}
"("                     {return(yytext[0]);}
")"                     {return(yytext[0]);}
.                       {return (yytext[0]); /*default action*/}

%%

Can someone please help me figure out, what is causing the issue. The pattern is also unindented properly. thanks for your help.

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1 回答 1

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这是有效的flex输入，但它是无效的jflex。由于包含的代码是 inC而不是Java，我不清楚您为什么要使用jflex，但是如果您的意图是将扫描仪移植到Java您可能需要阅读JFlex 手册中有关移植的部分。

特别是，JFlex输入中的部分与flex：

        flex                                 JFlex

definitions and declarations            user code
%%                                      %%
rules                                   declarations
%%                                      %%
user code                               definitions and rules

因此，您的定义和规则位于文件的正确部分flex，但不适用于JFlex文件。（JFlex只是将第一部分复制到输出中，因此它无法识别由于将 flex 声明放在 JFlex 期望有效用户代码的位置而导致的各种语法错误。）

此外，JFlex定义的形式name = pattern是而不是name pattern，因此一旦您整理好文件的顺序，您还需要添加等号。和。当然，C重写Java.

于 2014-10-23T17:24:39.013 回答