Re: newbie here ask about qi::_val and semantic action

Elaborate.  The following works.

#include <iostream>
#include <string>

#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/qi.hpp>

int main() {
     std::string s = "1234.56789";
     double d;

     std::string::iterator first = s.begin();
     std::string::iterator last = s.end();

     namespace qi = boost::spirit::qi;
     bool r = qi::phrase_parse(first, last, qi::double_ [qi::_val = 
qi::_1], qi::space, d);

     if (!r || first != last) {
         std::cerr << "Error while parsing.  Rest: " << 
std::string(first, last) << "\n";
     }
     std::cout << "Success! " << d << "\n";
}


On 09/07/18 03:40, Yi Leong wrote:
> Hi,
> I set qi::_val in semantic action function , but it does not work.
> Is the placeholder _val only usable in lambda expression?
> 
> 
> 
> 
> 
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