Flex Bison: Building C Compiler - Line number in error message

Question

When I try to print my line number in my yyerror function, I get an error. I'm working on OSX.

(line number in compiler.l)

%{

#include "compiler.tab.h"
int lineNumber = 1;

%}
%%

int { return INT; }
float { return FLOAT; }
void { return VOID; }
do { return DO; }
while { return WHILE; }
if { return IF; }
return { return RETURN; }
else { return ELSE; }
\/\/(.)* { return COMMENT; }
\/\*(.)*\*\/ { return COMMENT; }
[a-zA-Z][a-zA-Z0-9_]* { return IDENT; }
[0-9]+\.[0-9]+ { sscanf(yytext, "%lf", &yylval.reell); return FVAL; }
[0-9]+ { yylval.integer = atoi(yytext); return IVAL; }
\( { return OPA; }
\) { return CPA; }
\{ { return OB; }
\} { return CP; }
\; { return SEMICOLON; }
\, { return COMMA; }
\! { return NOT; }
\-\- { return DECREMENT; }
\+\+ { return INCREMENT; }
\<\< { return LSHIFT; }
\=\= { return EQUALS; }
\<\= { return LTOE; }
\>\= { return GTOE; }
\&\& { return AND; }
\|\| { return OR; }
\= { return ASSIGNMENT; }
\< { return LT; }
\> { return GT; }
\/ { return DIVIDE; }
\* { return MULTIPLY; }
\+ { return PLUS; }
\- { return MINUS; }
[ ]+ { return BLNK; }
[\n]* { ++lineNumber; return NL; }

%%

compiler.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "compiler.h"

extern int lineNumber;

int main (void)
{
    yyparse();
    return 0;
}

void yyerror(char * str)
{
    fprintf(stderr, "Error: %s, Line %d\n", str, lineNumber);
}

I get the following error message:

Undefined symbols for architecture x86_64: "_lineNumber", referenced from: _yyerror in compiler.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

This is the command (shell file) I use to compile:

#!/bin/bash

flex  compiler.l
bison -d compiler.y

gcc -g -c compiler.tab.c -o compiler_y.o
gcc -g -Wall -std=c99 -c lex.yy.c
gcc -g -c compiler.tab.c -o compiler_y.o

gcc -g -Wall -std=c99 -c compiler.c
gcc -g -o compiler compiler.o compiler_y.o lex.yy.o -lm -lfl

Please be careful when tagging. Flex is used for the Apache/Adobe UI Framework. Gnu-flex is used for the lexical analyzer. — JeffryHouser
Where in the .l file did you put that line? It seems like you're not defining it as an external symbol (or, if you are, you're not including the compiled lexer in your executable). — rici
@rici I put the whole code of the compiler.l. Hope this helps. Thanks all for your help. — hapablap
How do you compile/link? You may compile lex output as C++, then it will have different signature. You may forget to link your parser module altogether. — Valeri Atamaniouk
Your flex file looks ok, so I agree with @ValeriAtamaniouk that you've probably got an error in your compile/link commands. — rici

Bryan Olivier Bryan Olivier · Accepted Answer · 2013-03-15T13:43:23

You can use %option yylineno in your flex source and then the variable int yylineno will give the line-number of your current token. Beware not to use yylineno from the grammar (bison/yacc) as the tokenizer in general is ahead of the parser. If you want to use line numbers in the parser, typically the line numbers are attached to the tokens, so the parser has access through the tokens.

The error message is likely caused by not linking in compiler.tab.o, obtained from compiler.l by running flex on it and then passing it through the C-compiler.

Flex Bison: Building C Compiler - Line number in error message

1 Answers