Re: [Boost-users] [Spirit 2] on_error to string

Subject: Re: [Boost-users] [Spirit 2] on_error to string
From: TONGARI (tongari95_at_[hidden])
Date: 2011-04-06 10:43:32

2011/4/6 Vincent Agnus <vincent.agnus_at_[hidden]>

> Hi,
>
>  I have some trouble to retreive error parsing information using
> qi::on_error<fail> to work on a std::string.
>
> The documentation propose the following code :
>
> on_error<fail>
> (
>   start
>   , std::cout
>     << val("constituent: expected ")
>     << _4                               // what failed?
>     << val(" here: \"")
>     << construct<std::string>(_3, _2)   // iterators to error-pos, end
>     << val("\"")
>     << std::endl
> );
>
>
>  * On my First attempt. I have define a class member (std::stringstream
>  m_error) in my grammar class  and replace std::cout by phx::ref(m_error).
> But this code generate a compilation error
>

Seems like a Phoenix bug to me. Here's a workaround:
    (ostream&)m_error << ...

> * For the second attempt, I declare class member m_error as std::string and
> use this error handler:
>
>
> namespace qi = boost::spirit::qi;
> namespace phx = boost::phoenix;
>
>
> on_error< qi::fail>
> (
>    start
>    , phx::ref(m_error)
>       = (    phx::construct<std::string>(phx::val("Error! Expecting "))
>            // + qi::_4      REMARK1
>            + phx::construct<std::string>( phx::val(" here: \"") )
>            + phx::construct<std::string>(qi::_3, qi::_2)
>            + phx::construct<std::string>( phx::val("\"") )
>         )
>       );
>
> that's work perfectly. On error my string is correctly filled. But my
> problem is that I can't get the expected token (_4) (REMARK1), If I
> uncomment line REMARK1, I get a compilation error, same result using the
> code    phx::construct<std::string>(qi::_4).
>
> How can a get qi::_4 as string ?
>

phx::bind(&boost::spirit::info::tag, qi::_4)

> Can any one with kindness help me?
>

HTH