2011/4/6 TONGARI <tongari95@gmail.com>
2011/4/6 Vincent Agnus <vincent.agnus@ircad.fr>
How can a get qi::_4 as string ?

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

Well, this may or may not be what you want, though...

qi::_4 here stands for a boost::spirit::info object which seems not documented yet.
Anyway, it's not a string, but it's outputable (traverse through its value, a tree structure), so its tag member (a utf8_string) is not identical to what will be output, you can see your BOOST_ROOT/boost/spirit/home/support/info.hpp