CODEWITHSUNDEEP
cyacc
ora
ora

Reputation: 163

New line with yacc generated parser is ignored

This interpreter on ubuntu 20.04 has problem with new lines.

s1.l

%%
(a|b)*  { strcpy(yylval.string, yytext);
      return AB; 
        }
z   return Z;
'\n'    return yytext[0];
.   return yytext[0];
%%

s1.y

%{
#include <stdio.h>
#include <string.h>
#define check(first, two) \
        if (strcmp(first, two)) \
            fprintf(stderr, " -------- no word of language S1\n"); \
        else \
            fprintf(stderr, " --------  word of language S1\n");
int yylex();
void yyerror();

%}
%union {
    char string[100];
}
%token Z
%token <string> AB

%%
word: AB Z AB '\n' { check($1, $3); }  
    | word AB Z AB '\n' { check($2, $4); } 
    | error '\n'
    ;
%%
#include "lex.yy.c"
void yyerror(char *s)
{
    fprintf(stderr, "no word of language S1\n"); 
}

When I am running the interpreter the new line character is not recognized.

./s1
aazbb

Upvotes: 0

Views: 291

Answers (2)

Chris Dodd
Chris Dodd

Reputation: 126498

lex does not treat ' as a special character (denoting a single character), so when you have a pattern '\n' it matches that literal 3-character sequence. Use "\n" (or just \n) instead.

Upvotes: 3

P. PICARD
P. PICARD

Reputation: 386

Your pattern is a new line surrounded by simple quotes, then lex (or flex) is expecting that to return a new line to the parser and it is normal that the new line is not recognized. You should simply remove the simple quotes as follows:

%%
(a|b)*  { strcpy(yylval.string, yytext);
      return AB; 
        }
z   return Z;
\n    return yytext[0];
.   return yytext[0];
%%

Upvotes: 0

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