提升：：精神：：气：:p屁股 --> 没有结果

Question

考虑以下代码:

namespace qi  = boost::spirit::qi;
typedef qi::rule<
    std::string::const_iterator
> rule_type;
rule_type value_rule = +qi::char_ - ( '[' | qi::eoi );
std::string input( "Hello World" );
std::string value0, value1;
bool b0 = qi::parse( input.begin( ),
                     input.end( ),
                     value_rule,
                     value0 );
bool b1 = qi::parse( input.begin( ),
                     input.end( ),
                     +qi::char_ - ( '[' | qi::eoi ),
                     value1 );

结果:

b0 = true  
b1 = true  
value0 = ""  
value1 = "Hello World"

我很困惑为什么结果不同。要获得相同的结果，qi::规则类型的正确定义是什么?

Answer 1

您忘记让规则声明其公开的属性类型了:

typedef qi::rule<std::string::const_iterator, std::string()> rule_type;

Live On Coliru

#include <boost/spirit/include/qi.hpp>
namespace qi  = boost::spirit::qi;

int main() 
{
    std::string const input( "Hello World" );
    {
        typedef qi::rule<std::string::const_iterator, std::string()> rule_type;
        rule_type value_rule = +qi::char_ - ( '[' | qi::eoi );
        std::string value;
        bool ok = qi::parse( input.begin( ),
                input.end( ),
                value_rule,
                value );
        std::cout << std::boolalpha << ok << "t" << value << "n";
    }
    {
        std::string value;
        bool ok = qi::parse( input.begin( ),
                input.end( ),
                +qi::char_ - ( '[' | qi::eoi ),
                value );
        std::cout << std::boolalpha << ok << "t" << value << "n";
    }
}

输出

true    Hello World
true    Hello World