Using boost::spirit to match words

I want to create a parser that will match exactly two alphanumeric words from a string, such as:

message1 message2

and then save that into two variables of type std::string.

I've read this previous answer which seems to work for an endless amount of repetitions, which uses the following parser:

+qi::alnum % +qi::space

However when I try to do this:

 bool const result = qi::phrase_parse(
            input.begin(), input.end(),
            +qi::alnum >> +qi::alnum,
            +qi::space,
            words
    );

the words vector contains every single letter in a different string:

't'
'h'
'i'
's'
'i'
's'

This is extremely counter-intuitive, and I'm not sure as to why it's happening. Could someone please explain that?

Also, can I have two predefined strings to be populated instead of a std::vector?

Final note: I would like to avoid the using statement, as I would like to have every namespace clearly defined to help me understand how Spirit works.

Solution

Yes, but the skipper ignores the whitespace before you can act on it.

Use lexeme to control the skipper:

bool const result = qi::phrase_parse(
        input.begin(), input.end(),
        qi::lexeme [+qi::alnum] >> qi::lexeme [+qi::alnum],
        qi::space,
        words
);

Note the skipper should be qi::space instead of +qi::space.