野牛令牌是字符串的其余部分 [英] Bison token is rest of the string

问题描述

我写了一个flex和野牛， 我遇到了一个问题，该问题可以通过以下程序进行说明.

I have written a flex and bison, I am facing a problem which is illustrated via the below program.

该程序用于解析由等号(=)分隔的键/值对 我希望我的野牛脚本能将键和值标记化并打印出来.

The program is intended to parse the key-value pairs separated by an equals (=) sign I am hoping that my bison script tokenizes the key and values and prints them.

下面是我的flex程序的代码段

Below is the snippet of my flex program

%{
    /* file : kvp.l */
    #include <stdio.h>
    #define YYSTYPE char*
    #include "kvp.tab.h"
%}

%%
[a-zA-Z0-9][_a-zA-Z0-9]*    {
                                yylval=yytext;
                                return IDENTIFIER;
                            }
"="                         {
                                yylval=yytext;
                                return EQUALS_OP;
                            }
.                           ; /* Do Nothing */
%%

int yywrap()
{
    return 1;
}

下面是Bison程序

%{
    /* file : kvp.y */
    #include <stdio.h>
    #include <stdlib.h>

    /* interface to the lexer */
    int yylex();
    int yyerror (char const *s);
%}

%token IDENTIFIER EQUALS_OP
%start stmt

%%
stmt: stmt pair | pair;
pair: IDENTIFIER EQUALS_OP IDENTIFIER
                                        {
                                            printf("YACC : Key     = \"%s\"\n", $1);
                                            printf("YACC : Equals  = \"%s\"\n", $2);
                                            printf("YACC : Value   = \"%s\"\n", $3);
                                        };
%%

int yyerror (char const *s)
{
    fprintf (stderr, "Error String = \"%s\"\n", s);
}

int main( int argc, char* argv[])
{
    yyparse();
    return 0;
}

我从该程序中得到的结果如下.

The result which I am getting out of this program is as below.

student@debian:~/stack-overflow$ flex kvp.l
student@debian:~/stack-overflow$ bison -d --file-prefix=y kvp.y
student@debian:~/stack-overflow$ gcc lex.yy.c  y.tab.c -o parser
student@debian:~/stack-overflow$ ./parser 
earth=planet
YACC : Key     = "earth=planet"
YACC : Equals  = "=planet"
YACC : Value   = "planet"

可以看到正在打印的令牌是不正确的，所以从令牌开始的整个字符串都被打印了. 请告诉我该程序在哪里出错.

As one can see the tokens which are being printed is not right, the entire string beginning from the token is being printed. Please tell me where I am going wrong in this program.

推荐答案

问题是您正在保存指向yytext的指针，该指针随后在Flex扫描仪中进行了更新.如果将其更改为将字符串的副本保存在yytext中，则将获得更一致的结果，例如，

The problem is that you are saving a pointer to yytext, which is later updated in the flex scanner. If you change that to save a copy of the string in yytext, you will get more consistent results, e.g.,

yylval = strdup(yytext);

而不是

yylval = yytext;

进一步阅读:

• 回复:[Flex-help] yytext返回为char **
• 21.3关于yytext和内存的注释

• Re: [Flex-help] yytext return as char*
• 21.3 A Note About yytext And Memory

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