Re: $x value lost?

[Bruce Lilly]

Mhaxx wrote:
> Why does parser loose values?
>
> EXAMPLE:
>
> My scanner:
> ...
> {kw_program}    { free(yylval.string); yylval.string = strdup(yytext);
> return PROGRAM; }
> {kw_return}    { free(yylval.string); yylval.string = strdup(yytext); return
> RETURN; }
> {kw_end}    { free(yylval.string); yylval.string = strdup(yytext); return
> END; }
>
> My parser:
> start: PROGRAM RETURN END;    { printf($1); printf($2); printf($3); }
>
> If the input is "program Return end" then the output is "endend"!!! Why?!?
>
> I think $1 and $2 were lost during the process... there's something I can't
> understand...

First, you wiped out the values with free() in the lexical analyzer.
Second, beware using printf like that -- if your input is %s %d %x
you'll have Big Problems.  Try:

{kw_program} { yylval.string = strdup(yytext); return PROGRAM; }
{kw_return}  { yylval.string = strdup(yytext); return RETURN; }
{kw_end}     { yylval.string = strdup(yytext); return END; }

start: PROGRAM RETURN END;    {
    if ($1) { puts($1); free($1); }
    if ($2) { puts($2); free($2); }
    if ($3) { puts($3); free($3); }
}