Re: yyerror() location tracking

[Luca]

Il 17/01/2010 7.18, Tom Stellard ha scritto:
> Hi,
>
> I am trying to add line numbers to my parser's error messages.  I have
> included the options, %locations and %define api.pure in my bison
> definition file, but it seems to be generating yyerror with this signature:
> yyerror(const char *msg);
> instead of the signature I am expecting:
> yyerror (YYLTYPE *locp, const char * msg)
> I have attached the bison definition file I am trying to use.
> Thanks.
>
> -Tom
>
>
> _______________________________________________
> address@hidden http://lists.gnu.org/mailman/listinfo/help-bison
bison manual reports
(http://www.gnu.org/software/bison/manual/bison.html#Error-Reporting):

if '%locations %define api.pure' is passed then the prototypes for 
|yyerror| are:

     void yyerror (char const *msg);                 /* Yacc parsers.  */
     void yyerror (YYLTYPE *locp, char const *msg);  /* GLR parsers.   */



so bison generates the right signature (yyerror(const char *msg);), 
because you don't specify a GLR parser (don't use GLR parser unless you 
really need it).



If you need to track line error, you can access to the line using yylloc 
(YYLTYPE struct):

void yyerror (const char *s)
{

        fprintf(stderr, "%s line:%d", s,yylloc.first_line);
}


Of course your lexer, for each token matched, has to fill yylloc;
typically using flex you have to define a macro (YY_USER_ACTION) like 
the following one:

#define YY_USER_ACTION {yylloc.first_line = yylineno; \
        yylloc.first_column = colnum;                 \
        colnum=colnum+yyleng;                         \
        yylloc.last_column=colnum;                    \
        yylloc.last_line = yylineno;}

see flex manual for YY_USER_ACTION:
http://flex.sourceforge.net/manual/Misc-Macros.html#Misc-Macros
and also for yylineno (using %option yylineno flex will manage line 
number for you):
http://flex.sourceforge.net/manual/Options-Affecting-Scanner-Behavior.html#Options-Affecting-Scanner-Behavior

The parser generated by bison, for each rule, merges the locations using 
YYLLOC_DEFAULT macro.
If you need you can redefine YYLTYPE and YYLLOC_DEFAULT according to 
your purposes.

Luca