c++ - 尝试使用 boost::spirit 解析字符串中的一个整数时出现编译器错误

Question

我正在尝试解析一个字符串，该字符串旁边包含一些特殊的单词和整数。设特殊词为“HHH”。需要跳过前面的数据，解析后面的数据。这是我的尝试:

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

namespace qi = boost::spirit::qi;
int main ()
{
    std::string input = "asd eee rrr HHH 456";
    std::string::iterator strbegin = input.begin();
    int result;
    bool ok = qi::phrase_parse(
            strbegin, input.end(),
            (*(qi::char_ - qi::lit("HHH")) >> qi::lit("HHH") >> qi::int_),
            qi::space,                  
            result);                               

    std::cout << ok << std::endl;
    std::cout << result << std::endl;
}

我收到此错误消息:

main.cpp:14:   instantiated from here                                                                                                                                                                
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp:454: error: no matching function for call to mpl_::void_::void_(int)                                                            
/usr/include/boost/mpl/void.hpp:29: note: candidates are: mpl_::void_::void_()                                                                                                                       
/usr/include/boost/mpl/void.hpp:29: note:                 mpl_::void_::void_(const mpl_::void_&)                                                                                                     
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp: In static member function static bool boost::spirit::qi::detail::extract_int<T, Radix, 1u, -0x00000000000000001, Accumulator, Accumulate>::parse_main(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, Accumulator = boost::spirit::qi::detail::positive_accumulator<10u>, bool Accumulate = false]:                                                   
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp:501:   instantiated from static bool boost::spirit::qi::detail::extract_int<T, Radix, 1u, -0x00000000000000001, Accumulator, Accumulate>::parse(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, Accumulator = boost::spirit::qi::detail::positive_accumulator<10u>, bool Accumulate = false]                                                           
/usr/include/boost/spirit/home/qi/numeric/numeric_utils.hpp:108:   instantiated from static bool boost::spirit::qi::extract_int<T, Radix, MinDigits, MaxDigits>::call(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, unsigned int MinDigits = 1u, int MaxDigits = -0x00000000000000001]                                                                                                                                  
/usr/include/boost/spirit/home/qi/numeric/int.hpp:98:   instantiated from bool boost::spirit::qi::int_parser_impl<T, Radix, MinDigits, MaxDigits>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, unsigned int MinDigits = 1u, int MaxDigits = -0x00000000000000001]                                                                                                                            
/usr/include/boost/spirit/home/qi/detail/fail_function.hpp:38:   instantiated from bool boost::spirit::qi::detail::fail_function<Iterator, Context, Skipper>::operator()(const Component&, Attribute&) const [with Component = boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, Attribute = mpl_::void_, Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >]                                                                                                                                                                  
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:171:   instantiated from bool boost::spirit::detail::any_if(const First1&, const First2&, const Last&, F&, mpl_::false_) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, First1 = boost::fusion::cons_iterator<const boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> >, Last = boost::fusion::cons_iterator<const boost::fusion::nil>, First2 = boost::fusion::vector_iterator<boost::fusion::vector1<int&>, 1>, F = boost::spirit::qi::detail::fail_function<__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, const boost::fusion::unused_type, boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> > >]                                                                                                                                                                                    
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:171:   instantiated from bool boost::spirit::detail::any_if(const First1&, const First2&, const Last&, F&, mpl_::false_) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, First1 = boost::fusion::cons_iterator<const boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > >, Last = boost::fusion::cons_iterator<const boost::fusion::nil>, First2 = boost::fusion::vector_iterator<boost::fusion::vector1<int&>, 1>, F = boost::spirit::qi::detail::fail_function<__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, const boost::fusion::unused_type, boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> > >]                                                                                                  
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:171:   instantiated from bool boost::spirit::detail::any_if(const First1&, const First2&, const Last&, F&, mpl_::false_) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, First1 = boost::fusion::cons_iterator<const boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > > >, Last = boost::fusion::cons_iterator<const boost::fusion::nil>, First2 = boost::fusion::vector_iterator<boost::fusion::vector1<int&>, 0>, F = boost::spirit::qi::detail::fail_function<__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, const boost::fusion::unused_type, boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> > >]                       
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:186:   instantiated from bool boost::spirit::any_if(const Sequence1&, Sequence2&, F, Pred) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, Sequence1 = boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > >, Sequence2 = boost::fusion::vector1<int&>, F = boost::spirit::qi::detail::fail_function<__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, const boost::fusion::unused_type, boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> > >]                                                                                                                                                                                      
/usr/include/boost/spirit/home/qi/operator/sequence_base.hpp:81:   instantiated from bool boost::spirit::qi::sequence_base<Derived, Elements>::parse_impl(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&, mpl_::false_) const [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, Attribute = int, Derived = boost::spirit::qi::sequence<boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > > >, Elements = boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > >]                      
/usr/include/boost/spirit/home/qi/operator/sequence_base.hpp:115:   instantiated from bool boost::spirit::qi::sequence_base<Derived, Elements>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::phrase_parse(Iterator&, Iterator, const Expr&, const Skipper&, boost::spirit::qi::skip_flag::enum_t, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Expr = boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::dereference, boost::proto::argsns_::list1<const boost::proto::exprns_::expr<boost::proto::tag::minus, boost::proto::argsns_::list2<const boost::spirit::terminal<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&>, 1l>&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&, const boost::spirit::terminal<boost::spirit::tag::int_>&>, 2l>, Skipper = boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, 0l>, Attr = int]::skipper_type, Attribute = int, Derived = boost::spirit::qi::sequence<boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > > >, Elements = boost::fusion::cons<boost::spirit::qi::kleene<boost::spirit::qi::difference<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >, boost::spirit::qi::literal_string<const char (&)[4], true> > >, boost::fusion::cons<boost::spirit::qi::literal_string<const char (&)[4], true>, boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> > >]                                                                                  
/usr/include/boost/spirit/home/qi/parse.hpp:114:   instantiated from bool boost::spirit::qi::phrase_parse(Iterator&, Iterator, const Expr&, const Skipper&, boost::spirit::qi::skip_flag::enum_t, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Expr = boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::dereference, boost::proto::argsns_::list1<const boost::proto::exprns_::expr<boost::proto::tag::minus, boost::proto::argsns_::list2<const boost::spirit::terminal<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&>, 1l>&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&, const boost::spirit::terminal<boost::spirit::tag::int_>&>, 2l>, Skipper = boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, 0l>, Attr = int]                                                 
/usr/include/boost/spirit/home/qi/parse.hpp:132:   instantiated from bool boost::spirit::qi::phrase_parse(Iterator&, Iterator, const Expr&, const Skipper&, Attr&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Expr = boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::shift_right, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tag::dereference, boost::proto::argsns_::list1<const boost::proto::exprns_::expr<boost::proto::tag::minus, boost::proto::argsns_::list2<const boost::spirit::terminal<boost::spirit::tag::char_code<boost::spirit::tag::char_, boost::spirit::char_encoding::standard> >&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&>, 1l>&, const boost::proto::utility::literal<const char (&)[4], boost::proto::domainns_::default_domain>&>, 2l>&, const boost::spirit::terminal<boost::spirit::tag::int_>&>, 2l>, Skipper = boost::spirit::standard::space_type, Attr = int]                                           
main.cpp:14:   instantiated from here                                                                                                                                                                
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp:454: error: no matching function for call to mpl_::void_::void_(int)                                                            
/usr/include/boost/mpl/void.hpp:29: note: candidates are: mpl_::void_::void_()                                                                                                                       
/usr/include/boost/mpl/void.hpp:29: note:                 mpl_::void_::void_(const mpl_::void_&)                                                                                                     
In file included from /usr/include/boost/spirit/home/qi/auxiliary/attr.hpp:18,                                                                                                                       
                 from /usr/include/boost/spirit/home/qi/auxiliary.hpp:19,                                                                                                                            
                 from /usr/include/boost/spirit/home/qi.hpp:15,                                                                                                                                      
                 from /usr/include/boost/spirit/include/qi.hpp:16,                                                                                                                                   
                 from main.cpp:2:                                                                                                                                                                    
/usr/include/boost/spirit/home/qi/detail/assign_to.hpp: In static member function static void boost::spirit::traits::assign_to_attribute_from_value<Attribute, T, Enable>::call(const T&, Attribute&) [with Attribute = mpl_::void_, T = int, Enable = void]:                                                                                                                                           
/usr/include/boost/spirit/home/qi/detail/assign_to.hpp:99:   instantiated from void boost::spirit::traits::assign_to(const T&, Attribute&) [with T = int, Attribute = mpl_::void_]                 
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp:448:   instantiated from static bool boost::spirit::qi::detail::extract_int<T, Radix, 1u, -0x00000000000000001, Accumulator, Accumulate>::parse_main(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, Accumulator = boost::spirit::qi::detail::negative_accumulator<10u>, bool Accumulate = false]                                                      
/usr/include/boost/spirit/home/qi/numeric/detail/numeric_utils.hpp:501:   instantiated from static bool boost::spirit::qi::detail::extract_int<T, Radix, 1u, -0x00000000000000001, Accumulator, Accumulate>::parse(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, Accumulator = boost::spirit::qi::detail::negative_accumulator<10u>, bool Accumulate = false]                                                           
/usr/include/boost/spirit/home/qi/numeric/numeric_utils.hpp:106:   instantiated from static bool boost::spirit::qi::extract_int<T, Radix, MinDigits, MaxDigits>::call(Iterator&, const Iterator&, Attribute&) [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, unsigned int MinDigits = 1u, int MaxDigits = -0x00000000000000001]                                                                                                                                  
/usr/include/boost/spirit/home/qi/numeric/int.hpp:98:   instantiated from bool boost::spirit::qi::int_parser_impl<T, Radix, MinDigits, MaxDigits>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >, Attribute = mpl_::void_, T = int, unsigned int Radix = 10u, unsigned int MinDigits = 1u, int MaxDigits = -0x00000000000000001]                                                                                                                            
/usr/include/boost/spirit/home/qi/detail/fail_function.hpp:38:   instantiated from bool boost::spirit::qi::detail::fail_function<Iterator, Context, Skipper>::operator()(const Component&, Attribute&) const [with Component = boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, Attribute = mpl_::void_, Iterator = __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Context = const boost::fusion::unused_type, Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> >]                                                                                                                                                                  
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:171:   instantiated from bool boost::spirit::detail::any_if(const First1&, const First2&, const Last&, F&, mpl_::false_) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, First1 = boost::fusion::cons_iterator<const boost::fusion::cons<boost::spirit::qi::int_parser_impl<int, 10u, 1u, -0x00000000000000001>, boost::fusion::nil> >, Last = boost::fusion::cons_iterator<const boost::fusion::nil>, First2 = boost::fusion::vector_iterator<boost::fusion::vector1<int&>, 1>, F = boost::spirit::qi::detail::fail_function<__gnu_cxx::__normal_iterator<char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, const boost::fusion::unused_type, boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::standard> > >]                                                                                                                                                                                    
/usr/include/boost/spirit/home/support/algorithm/any_if.hpp:171:   instantiated from bool boost::spirit::detail::any_if(const First1&, const First2&, const Last&, F&, mpl_::false_) [with Pred = boost::spirit::traits::attribute_not_unused<const boost::fusion::unused_type, __gnu_cxx::__normal_iterator<

Answer 1

初始问题中的语法可以分解为具有以下属性:

(*(qi::char_ - qi::lit("HHH")) >> qi::lit("HHH") >> qi::int_)
~~~~~~~~~~ string ~~~~~~~~~~~~    ~~~ unused ~~~    ~~ int ~~

如果您不需要string 属性的结果，那么可以使用omit[] 解析指令来忽略解析器的属性。例如，以下使用 omit[] 忽略上面的 string 属性，导致解析器仅提供 int 属性。

(qi::omit[*(qi::char_ - qi::lit("HHH"))] >> qi::lit("HHH") >> qi::int_)
~~~~~~~~~~~~~~~~ unused ~~~~~~~~~~~~~~~~    ~~~ unused ~~~    ~~ int ~~

---

这是一个基于原始代码的完整的example:

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

namespace qi = boost::spirit::qi;
int main ()
{
    std::string input = "asd eee rrr HHH 456";
    std::string::iterator strbegin = input.begin();
    int result;
    bool ok = qi::phrase_parse(
            strbegin, input.end(),
            (qi::omit[*(qi::char_ - qi::lit("HHH"))] >> qi::lit("HHH")
              >> qi::int_),
            qi::space,                  
            result);                               

    std::cout << ok << std::endl;
    std::cout << result << std::endl;
}

产生以下输出:

1
456