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c++bisonyacclexflex-lexer

Bison : Line number included in the error messages

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.
Solution

  • 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! :-)