Re: [Spirit] '_' parsed as '\0' with qi::phrase_parse

From: Olaf van der Spek (ml_at_[hidden])
Date: 2022-07-19 06:57:58

On Mon, Jul 18, 2022 at 11:01 PM Seth via Boost <boost_at_[hidden]> wrote:
>
> A literal b in a parser expression created `qi::lit(b)`. `qi::lit` does not "have" (synthesize/expose) an attribute. You want either `qi::alpha | qi::char_("._")`, or `qi::char_("a-zA-Z0-9_.")` or even (as you're in a lexeme anyways) `raw[alpha >> *(alnum|'.'|'_')]` because for `raw[]` the synthesized attribute is the source iterator range.
>
> First fix: http://coliru.stacked-crooked.com/a/c5d9ee594370ac91
>
> Seeing that your `identifier` is a lexeme, you should just drop the skipper (see https://stackoverflow.com/a/17073965/85371).
>
> In the absense of semantic actions `%=` is redundant.
>
> I don't recommend using classic spirit features in 2022.
>
> All in all: https://godbolt.org/z/r6MPvK5aK

Hi Seth,

Thanks!
It's old, untouched code, hence the use of classic. I still don't get
why it's returning "a\0b" though, where does the \0 come from?
The code must've worked in the past, was the behavior of classic
spirit changed? Or did I rely on undefined behavior?

Your code parses multiple identifiers instead of just one, is that on purpose?

Greetings,

Olaf

> On Mon, Jul 18, 2022, at 9:24 AM, Olaf van der Spek via Boost wrote:
> > Hi,
> >
> > The underscore is parsed as a null character. Is this expected. A bug?
> >
> > If a full repro is needed I can create one.
> >
> >
> >     qi::rule<iterator_t, std::string(), Skip> identifier;
> >     identifier %= lexeme[alpha >> *(alnum | '.' | '_')];
> >
> >     typedef boost::spirit::classic::position_iterator<const char*> iterator_t;
> >
> >     std::string s = "a_b blah";
> >     iterator_t is(s.c_str(), s.c_str() + s.size(), "<name>");
> >
> >     std::string out;
> >     bool res = qi::phrase_parse(is, iterator_t(), identifier, skip, out);
> >     if (!res && is != iterator_t()) error_handler_::err(is);
> >     cout << out.size() << "|" << out << "|\n";
> >     cout << int(out[0]) << " " << int(out[1]) << " " << int(out[2]) << "\n";
> >
> > Output:
> > // 3|ab|
> > // 97 0 98
> >
> > Greetings,
> > --
> > Olaf
> >
> > _______________________________________________
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>
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-- 
Olaf