Bison : Line number included in the error messages

Question

OK, so I suppose my question is quite self-explanatory.

I'm currently building a parser in Bison, and I want to make error reporting somewhat better.

Currently, I've set %define parse.error verbose (which actually gives messages like syntax error, unexpected ***********************, expecting ********************.

All I want is to add some more information in the error messages, e.g. line number (in input/file/etc)

My current yyerror (well nothing... unusual... lol) :

void yyerror(const char *str)
{
    fprintf(stderr,"\x1B[35mInterpreter : \x1B[37m%s\n",str);
}

---

P.S.

• I've gone through the latest Bison documentation, but I seem quite lost...
• I've also had a look into the %locations directive, which most likely is very close to what I need - however, I still found no complete working example and I'm not sure how this is to be used.

Answer 1

So, here I'm a with a step-by-step solution :

• We add the %locations directive in our grammar file (between %} and the first %%)
• We make sure that our lexer file contains an include for our parser (e.g. #include "mygrammar.tab.h"), at the top
• We add the %option yylineno option in our lexer file (between %} and the first %%)

And now, in our yyerror function (which will supposedly be in our lexer file), we may freely use this... yylineno (= current line in file being processed) :

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

Yep. Simple as that! :-)

Answer 2

Whats worked for me was adding extern int yylineno in .ypp file:

/* parser.ypp */
%{
    extern int yylineno;
%}

/* scanner.lex */
...
%option yylineno