[antlr-interest] ANTLR C empty strings and NULL ->chars

[Jim Idle]

I'll take a look tomorrow. Maybe there is an incorrect test somewhere.

Jim

On Dec 16, 2009, at 21:20, Matt Johnston <matt at ucc.asn.au> wrote:

> Hi,
>
> I'm hitting a problem relating to empty strings in ANTLR C
> 3.2, wondering if it's a bug in the C runtime or in how I'm
> using it.
>
> I have a rule that uses SETTEXT() to set the token's text to
> an empty string (see below).  Later on trying to use
> $STRING.text->chars in an imaginary node rewrite rule
> segfaults because ->chars on an empty string is NULL rather
> than "\0". In toStringSS() it uses newRaw() to create the
> string but no characters get appended.
>
> Should newRaw8() be setting ->chars to a one-byte
> null-valued array rather than NULL? I think the only place
> where it will matter is toStringSS(), the rest of the calls
> to newRaw() look like they'll call string->appendS() which
> will set the chars pointer to a null-terminated string.
>
> Cheers,
> Matt
>
>
>
> STRING
> @declarations
> {
>        pANTLR3_STRING tmp;
> }
>        : '"' ~('"')* '"'
>        {
>         // remove the string quotes from the token
>         tmp = GETTEXT();
>         SETTEXT(tmp->subString(tmp, 1, tmp->len-1));
>        }
>        ;
>
> Parsing "" sets the token's text to empty.
> (It's an ugly rule but it's a workaround for something else.)
>
> There's then something like:
>
> plainvalue
>   : STRING
>   -> ^(PLAINVALUE[$STRING.text->chars])
>
> It's then failing in the tree grammar when it tries to use
> $PLAINVALUE.text.
>
>
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