Yacc program giving error:"syntax error"

Question

I have the following config file that I need to parse.

[ main ]
e_type=0x1B

The lex(test.l) and yacc(test.y) files are given below

test.l

%option noyywrap
%option yylineno
%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "y.tab.h"

int yylinenu = 1;
int yycolno=1;

/**
 * Forward declerations
 **/
void Number ();
void HexaNumber ();
unsigned char getHexaLex (char c);
unsigned int strtol16 (char * str);


%}

%option nounput
%option noinput
%option case-insensitive

/*-----------------------------------------------------------------
   Some macros (standard regular expressions)
------------------------------------------------------------------*/

DIGIT       [0-9]
HEXALETTER  [a-fA-F]
HEXANUMBER  [0][x](({DIGIT}|{HEXALETTER})+)
NUM         {DIGIT}+
HEXA        ({DIGIT}|{HEXALETTER}|[*])
STR         \"[^\"]*\"
WSPACE      [ \t]*
NEWLINE     [\n\r]        

/*----------------------------------------------------------------
   The lexer rules
------------------------------------------------------------------*/
%%

e_type                   { yylval.str = yytext; return T_E_TYPE; }
main                     { yylval.str = yytext; return T_MAIN_SECTION;}
{HEXANUMBER}             { yylval.n = atoi(yytext);  HexaNumber(); return T_NUMBER; }
=                        { return T_EQUAL; }
"["                      { return T_OPEN_BRACKET; }
"]"                      { return T_CLOSE_BRACKET;}

[^\t\n\r]                { }
{WSPACE}                 { } /* whitespace: (do nothing) */
{NEWLINE}                {  
                            yylinenu++;
                            return T_EOL;
                         }

%%

void Number () {
    yylval.n = atol(yytext);
}

test.y

%{
#include <ctype.h>
#include <stdio.h>
#include <stdarg.h>
#include "y.tab.h"
#include "lex.h"

#define E_PARSE_DEBUG
#ifdef E_PARSE_DEBUG
// Some yacc (bison) defines
#define YYDEBUG 1       // Generate debug code; needed for YYERROR_VERBOSE
#define YYERROR_VERBOSE // Give a more specific parse error message 
#endif

#define E_DEBUG_STRINGIFY(x) #x
#define E_DEBUG_TOSTRING(x) E_DEBUG_STRINGIFY(x)
#define E_DEBUG_AT (__FILE__ ":" E_DEBUG_TOSTRING(__LINE__))

extern  int yyparse (void);
extern int yylinenu;
extern int yycolno;
void yyerror(const char *str)
{
  fprintf(stderr,"line: %d column: %d error: %s %s \n",yylinenu,yycolno,str,yylval.str);
}

int yywrap()
{
  return 1;
}

int main()
{
  printf("> "); 

  // open a file handle to a particular file:
  FILE *myfile = fopen("tmp.conf", "r");
  // make sure it is valid:
  if (!myfile) {
      printf("I can't open tmp.conf \n");
      return -1;
  }else
  {
    printf("opened config file \n");
  }
  // set lex to read from it instead of defaulting to STDIN:
  yyin = myfile;

  yyparse();

  return 0;
}
int lineno = 0;
%}

/*------------------------------------------------------------------
  Yacc declarations
------------------------------------------------------------------ */

/* The structure for passing value between lexer and parser */
/* In the lexer we know it by the name 'yylval'*/
%union {
   char *str;
   unsigned int n;
   void * distr;
   void * command;
}

%token T_E_TYPE T_HOSTID_TYPE T_MAIN_SECTION T_EQUAL T_OPEN_BRACKET T_CLOSE_BRACKET T_EOL
%token <str> STRING
%token <n> T_NUMBER
%type <n> number


%%
config_file
    : /* empty */
    {

    }
    | config_file config_file_section
    {

    }
    ;

config_file_section
    : T_OPEN_BRACKET T_MAIN_SECTION T_CLOSE_BRACKET attribute_list
    {

    }
    ; 

attribute_list
    : /* empty */
    {

    }
    | attribute_list attribute_pair
    {

    }
    ;
attribute_pair
    : T_E_TYPE T_EQUAL number
    {

    }
    ;

number
    : T_NUMBER
    {

    }
    ;
%%

I have an include lex.h file that is included in test.y

#ifndef _LEX_H_
#define _LEX_H_

#include <stdio.h>

#ifdef _LEX_CPP_
int lineno = 1; // line number count; this will be used for error messages later
#else
   // Import some variables
extern int lineno;
extern FILE *yyin;  // the input stream

// Function prototype
int yylex ();
#endif

endif

I compile the files as follows.

flex test.l
yacc -d  test.y
gcc lex.yy.c y.tab.c -Wall  -ll -o test -ldag

The binary test that I get is giving

> opened config file 
line: 1 column: 1 error: syntax error main

HEXANUMBER in your .l file needs to be surrounded by {} — o11c
First you need to trace which token you're getting the syntax error at. Include yytext in your syntax error message. — user207421
Note that identifiers beginning with an underscore and a capital letter are reserved for the implementation for any purpose; you should not create identifiers such as _LEX_H_ yourself. In general, and with only a slight overstatement, you should not create identifiers that start with an underscore. You may use system-defined identifiers that start with underscore, but should not try to create your own. You'll often get away with it anyway, but it's wise to avoid trouble. — Jonathan Leffler

Jonathan Leffler Jonathan Leffler · Accepted Answer · 2015-08-04T03:30:00

Your problem is the rule:

attribute_pair
    : T_E_TYPE '=' number

Your lexer returns T_EQUAL but the grammar expects '=' and the two are not equal. It was easy for me to spot; when I run the program, I get the report:

> opened config file 

error: syntax error, unexpected T_EQUAL, expecting '='

So it was remarkably easy to find the problem. The yacc I'm using is actually bison:

$ yacc --version
bison (GNU Bison) 2.3
…
$

When I fixed that, the error changed:

> opened config file 

error: syntax error, unexpected T_NUMBER, expecting NUMBER

Fixing that involved changing:

%token T_E_TYPE T_HOSTID_TYPE T_MAIN_SECTION T_EQUAL T_OPEN_BRACKET T_CLOSE_BRACKET
%token <str> STRING
%token <n> T_NUMBER

(Drop T_NUMBER from first line; change NUMBER to T_NUMBER in third line.) And also:

number
    : T_NUMBER

(Change NUMBER to T_NUMBER.)

With both those changes, you get a successful run (no output other than the open message, but no errors either).

Yacc program giving error:"syntax error"

endif

1 Answers