Question

%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "parser.h"
extern int yylval;
%}
%start E
%token number
%%
S   :E  {printf("%s",$1);}
    ;
E   :E PLUS T   {$$ = $1 + $3;}
    |T  {$$ = $1;}
    ;
T   :T STAR F   {$$ = $1 * $3;}
    |F  {$$ = $1;}
    ;
F   :LP E RP    {$$ = $2;}
    |number {$$ = $1;}
    ;
%%

yylex(){
    char ch;
    ch = getchar();

    switch(ch){
        case '+':
            return PLUS;
            break;
        case '*':
            return STAR;
            break;
        case '(':
            return LP;
            break;
        case ')':
            return RP;
            break;
        default:
            if(ch >= '0' && ch <= '9'){
                ch -= '0';
                yylval = ch;;
                return (number);
            }
            else
                return -1;
    }
}

void main(){
    yyparse();
}

下午，我正在做关于如何使用yacc的任务，问题是我不知道如何在.y文件中正确包含头文件。从我所看到的各种描述如何编写.y文件的页面来看，编写这个.y文件没有任何错误。所以，请帮助我！

这些是我收到的错误消息

embedded@embedded-P15xEMx:~/Project/Compiler$ yacc parser.y
parser.y:19.10-11: error: symbol LP is used, but is not defined as a token and has no rules
 F  :LP E RP    {$$ = $2;}
     ^^
parser.y:13.12-15: error: symbol PLUS is used, but is not defined as a token and has no rules
 E  :E PLUS T   {$$ = $1 + $3;}
       ^^^^
parser.y:19.15-16: error: symbol RP is used, but is not defined as a token and has no rules
 F  :LP E RP    {$$ = $2;}
          ^^
parser.y:16.12-15: error: symbol STAR is used, but is not defined as a token and has no rules
 T  :T STAR F   {$$ = $1 * $3;}
       ^^^^

这是我收录的头文件

#ifndef _PARSER_H_
#define _PARSER_H_

    #include <stdio.h>

    #define PLUS 1
    #define STAR 2
    #define LP 3
    #define RP 4
    #define number 5

#endif

Answer 1

令牌符号不能由您自己声明，您必须使用Yacc来执行此操作，例如

%token PLUS

等

YACC：使用符号****，但未定义为令牌且没有规则

1 个答案: