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

yeah, in the qi::double_[qi::_val = qi::_1] , the semantic action is a
lambda expression, but as the following:

#include <iostream>
#include <string>

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

void print_action(double f)
{
  qi::_val = qi::_1; // it does not work....
}

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_ [&print_action],
qi::space, d);

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

}

The above code gets compiling error, so  is the placeholder qi::_val
usable only in the lambda expression, right?

On Mon, Jul 9, 2018 at 10:06 AM, Henri Menke <[email protected]> wrote:

> 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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