使用boost :: spirit :: x3

Question

这是boost::spirit::x3关于boost::string_view和std::vector<std::string>的后续问题。

虽然我可以解析为std::vector<boost::string_view>（previous one），但解析成#include <iostream> #include <string> #include <boost/utility/string_view.hpp> namespace boost { namespace spirit { namespace x3 { namespace traits { template <typename It> void move_to(It b, It e, boost::string_view& v) { v = boost::string_view(b, std::size_t(std::distance(b,e))); } } } } } // namespace boost #include <boost/spirit/home/x3.hpp> namespace parser { namespace x3 = boost::spirit::x3; using x3::char_; using x3::raw; const auto str_vec = *(raw[ +~char_('_')] >> '_'); } int main() { std::string input = "hello_world_"; std::vector<boost::string_view> strVec; parse(input.data(), input.data()+input.size(), parser::str_vec, strVec); for(auto& x : strVec) { std::cout << x << std::endl; } } 时会出现以下编译错误：

In file included from /usr/local/include/c++/6.1.0/bits/stl_tempbuf.h:60:0,

                 from /usr/local/include/c++/6.1.0/bits/stl_algo.h:62,

                 from /usr/local/include/c++/6.1.0/algorithm:62,

                 from /usr/local/include/boost/utility/string_view.hpp:27,

                 from main.cpp:4:

/usr/local/include/c++/6.1.0/bits/stl_construct.h: In instantiation of 'void std::_Construct(_T1*, _Args&& ...) [with _T1 = boost::basic_string_view<char, std::char_traits<char> >; _Args = {const char&}]':

/usr/local/include/c++/6.1.0/bits/stl_uninitialized.h:75:18:   required from 'static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = const char*; _ForwardIterator = boost::basic_string_view<char, std::char_traits<char> >*; bool _TrivialValueTypes = false]'

/usr/local/include/c++/6.1.0/bits/stl_uninitialized.h:126:15:   required from '_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = const char*; _ForwardIterator = boost::basic_string_view<char, std::char_traits<char> >*]'

/usr/local/include/c++/6.1.0/bits/stl_uninitialized.h:281:37:   required from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = const char*; _ForwardIterator = boost::basic_string_view<char, std::char_traits<char> >*; _Tp = boost::basic_string_view<char, std::char_traits<char> >]'

/usr/local/include/c++/6.1.0/bits/stl_vector.h:1288:33:   required from 'void std::vector<_Tp, _Alloc>::_M_range_initialize(_ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = boost::basic_string_view<char, std::char_traits<char> >; _Alloc = std::allocator<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/c++/6.1.0/bits/stl_vector.h:1261:4:   required from 'void std::vector<_Tp, _Alloc>::_M_initialize_dispatch(_InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = boost::basic_string_view<char, std::char_traits<char> >; _Alloc = std::allocator<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/c++/6.1.0/bits/stl_vector.h:406:11:   [ skipping 9 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]

/usr/local/include/boost/spirit/home/x3/operator/detail/sequence.hpp:496:24:   required from 'static bool boost::spirit::x3::detail::parse_into_container_impl<boost::spirit::x3::sequence<L, R>, Context, RContext>::call(const parser_type&, Iterator&, const Iterator&, const Context&, RContext&, Attribute&) [with Iterator = const char*; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >; Left = boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >; Right = boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type>; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; boost::spirit::x3::detail::parse_into_container_impl<boost::spirit::x3::sequence<L, R>, Context, RContext>::parser_type = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >]'

/usr/local/include/boost/spirit/home/x3/core/detail/parse_into_container.hpp:287:74:   required from 'bool boost::spirit::x3::detail::parse_into_container(const Parser&, Iterator&, const Iterator&, const Context&, RContext&, Attribute&) [with Parser = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >; Iterator = const char*; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/boost/spirit/home/x3/operator/kleene.hpp:32:48:   required from 'bool boost::spirit::x3::kleene<Subject>::parse(Iterator&, const Iterator&, const Context&, RContext&, Attribute&) const [with Iterator = const char*; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >; Subject = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >]'

/usr/local/include/boost/spirit/home/x3/core/parse.hpp:35:68:   required from 'bool boost::spirit::x3::parse_main(Iterator&, Iterator, const Parser&, Attribute&) [with Iterator = const char*; Parser = boost::spirit::x3::kleene<boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> > >; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/boost/spirit/home/x3/core/parse.hpp:60:26:   required from 'bool boost::spirit::x3::parse(const Iterator&, Iterator, const Parser&, Attribute&) [with Iterator = const char*; Parser = boost::spirit::x3::kleene<boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> > >; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

main.cpp:36:75:   required from here

/usr/local/include/c++/6.1.0/bits/stl_construct.h:75:7: error: no matching function for call to 'boost::basic_string_view<char, std::char_traits<char> >::basic_string_view(const char&)'

     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }

       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from main.cpp:4:0:

/usr/local/include/boost/utility/string_view.hpp:82:23: note: candidate: constexpr boost::basic_string_view<charT, traits>::basic_string_view(const charT*) [with charT = char; traits = std::char_traits<char>] <near match>

       BOOST_CONSTEXPR basic_string_view(const charT* str)

                       ^~~~~~~~~~~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:82:23: note:   conversion of argument 1 would be ill-formed:

In file included from /usr/local/include/c++/6.1.0/bits/stl_tempbuf.h:60:0,

                 from /usr/local/include/c++/6.1.0/bits/stl_algo.h:62,

                 from /usr/local/include/c++/6.1.0/algorithm:62,

                 from /usr/local/include/boost/utility/string_view.hpp:27,

                 from main.cpp:4:

/usr/local/include/c++/6.1.0/bits/stl_construct.h:75:7: error: invalid conversion from 'char' to 'const char*' [-fpermissive]

     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }

       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from main.cpp:4:0:

/usr/local/include/boost/utility/string_view.hpp:85:23: note: candidate: constexpr boost::basic_string_view<charT, traits>::basic_string_view(const charT*, boost::basic_string_view<charT, traits>::size_type) [with charT = char; traits = std::char_traits<char>; boost::basic_string_view<charT, traits>::size_type = long unsigned int]

       BOOST_CONSTEXPR basic_string_view(const charT* str, size_type len)

                       ^~~~~~~~~~~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:85:23: note:   candidate expects 2 arguments, 1 provided

/usr/local/include/boost/utility/string_view.hpp:78:9: note: candidate: template<class Allocator> boost::basic_string_view<charT, traits>::basic_string_view(const std::__cxx11::basic_string<charT, traits, Allocator>&)

         basic_string_view(const std::basic_string<charT, traits,

         ^~~~~~~~~~~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:78:9: note:   template argument deduction/substitution failed:

In file included from /usr/local/include/c++/6.1.0/bits/stl_tempbuf.h:60:0,

                 from /usr/local/include/c++/6.1.0/bits/stl_algo.h:62,

                 from /usr/local/include/c++/6.1.0/algorithm:62,

                 from /usr/local/include/boost/utility/string_view.hpp:27,

                 from main.cpp:4:

/usr/local/include/c++/6.1.0/bits/stl_construct.h:75:7: note:   mismatched types 'const std::__cxx11::basic_string<char, std::char_traits<char>, Allocator>' and 'const char'

     { ::new(static_cast<void*>(__p)) _T1(std::forward<_Args>(__args)...); }

       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from main.cpp:4:0:

/usr/local/include/boost/utility/string_view.hpp:68:23: note: candidate: constexpr boost::basic_string_view<charT, traits>::basic_string_view(const boost::basic_string_view<charT, traits>&) [with charT = char; traits = std::char_traits<char>]

       BOOST_CONSTEXPR basic_string_view(const basic_string_view &rhs) BOOST_NOEXCEPT

                       ^~~~~~~~~~~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:68:23: note:   no known conversion for argument 1 from 'const char' to 'const boost::basic_string_view<char, std::char_traits<char> >&'

/usr/local/include/boost/utility/string_view.hpp:65:23: note: candidate: constexpr boost::basic_string_view<charT, traits>::basic_string_view() [with charT = char; traits = std::char_traits<char>]

       BOOST_CONSTEXPR basic_string_view() BOOST_NOEXCEPT

                       ^~~~~~~~~~~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:65:23: note:   candidate expects 0 arguments, 1 provided

In file included from /usr/local/include/c++/6.1.0/bits/char_traits.h:39:0,

                 from /usr/local/include/c++/6.1.0/ios:40,

                 from /usr/local/include/c++/6.1.0/ostream:38,

                 from /usr/local/include/c++/6.1.0/iostream:39,

                 from main.cpp:1:

/usr/local/include/c++/6.1.0/bits/stl_algobase.h: In instantiation of 'static _OI std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m(_II, _II, _OI) [with _II = const char*; _OI = boost::basic_string_view<char, std::char_traits<char> >*]':

/usr/local/include/c++/6.1.0/bits/stl_algobase.h:386:44:   required from '_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false; _II = const char*; _OI = boost::basic_string_view<char, std::char_traits<char> >*]'

/usr/local/include/c++/6.1.0/bits/stl_algobase.h:422:45:   required from '_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false; _II = const char*; _OI = __gnu_cxx::__normal_iterator<boost::basic_string_view<char, std::char_traits<char> >*, std::vector<boost::basic_string_view<char, std::char_traits<char> > > >]'

/usr/local/include/c++/6.1.0/bits/stl_algobase.h:455:8:   required from '_OI std::copy(_II, _II, _OI) [with _II = const char*; _OI = __gnu_cxx::__normal_iterator<boost::basic_string_view<char, std::char_traits<char> >*, std::vector<boost::basic_string_view<char, std::char_traits<char> > > >]'

/usr/local/include/c++/6.1.0/bits/vector.tcc:637:16:   required from 'void std::vector<_Tp, _Alloc>::_M_range_insert(std::vector<_Tp, _Alloc>::iterator, _ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const char*; _Tp = boost::basic_string_view<char, std::char_traits<char> >; _Alloc = std::allocator<boost::basic_string_view<char, std::char_traits<char> > >; std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<boost::basic_string_view<char, std::char_traits<char> >*, std::vector<boost::basic_string_view<char, std::char_traits<char> > > >; typename std::_Vector_base<_Tp, _Alloc>::pointer = boost::basic_string_view<char, std::char_traits<char> >*]'

/usr/local/include/c++/6.1.0/bits/stl_vector.h:1375:4:   required from 'void std::vector<_Tp, _Alloc>::_M_insert_dispatch(std::vector<_Tp, _Alloc>::iterator, _InputIterator, _InputIterator, std::__false_type) [with _InputIterator = const char*; _Tp = boost::basic_string_view<char, std::char_traits<char> >; _Alloc = std::allocator<boost::basic_string_view<char, std::char_traits<char> > >; std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<boost::basic_string_view<char, std::char_traits<char> >*, std::vector<boost::basic_string_view<char, std::char_traits<char> > > >; typename std::_Vector_base<_Tp, _Alloc>::pointer = boost::basic_string_view<char, std::char_traits<char> >*]'

/usr/local/include/c++/6.1.0/bits/stl_vector.h:1100:4:   [ skipping 12 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]

/usr/local/include/boost/spirit/home/x3/operator/detail/sequence.hpp:496:24:   required from 'static bool boost::spirit::x3::detail::parse_into_container_impl<boost::spirit::x3::sequence<L, R>, Context, RContext>::call(const parser_type&, Iterator&, const Iterator&, const Context&, RContext&, Attribute&) [with Iterator = const char*; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >; Left = boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >; Right = boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type>; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; boost::spirit::x3::detail::parse_into_container_impl<boost::spirit::x3::sequence<L, R>, Context, RContext>::parser_type = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >]'

/usr/local/include/boost/spirit/home/x3/core/detail/parse_into_container.hpp:287:74:   required from 'bool boost::spirit::x3::detail::parse_into_container(const Parser&, Iterator&, const Iterator&, const Context&, RContext&, Attribute&) [with Parser = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >; Iterator = const char*; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/boost/spirit/home/x3/operator/kleene.hpp:32:48:   required from 'bool boost::spirit::x3::kleene<Subject>::parse(Iterator&, const Iterator&, const Context&, RContext&, Attribute&) const [with Iterator = const char*; Context = boost::spirit::x3::unused_type; RContext = const boost::spirit::x3::unused_type; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >; Subject = boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> >]'

/usr/local/include/boost/spirit/home/x3/core/parse.hpp:35:68:   required from 'bool boost::spirit::x3::parse_main(Iterator&, Iterator, const Parser&, Attribute&) [with Iterator = const char*; Parser = boost::spirit::x3::kleene<boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> > >; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

/usr/local/include/boost/spirit/home/x3/core/parse.hpp:60:26:   required from 'bool boost::spirit::x3::parse(const Iterator&, Iterator, const Parser&, Attribute&) [with Iterator = const char*; Parser = boost::spirit::x3::kleene<boost::spirit::x3::sequence<boost::spirit::x3::raw_directive<boost::spirit::x3::plus<boost::spirit::x3::negated_char_parser<boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char> > > >, boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, boost::spirit::x3::unused_type> > >; Attribute = std::vector<boost::basic_string_view<char, std::char_traits<char> > >]'

main.cpp:36:75:   required from here

/usr/local/include/c++/6.1.0/bits/stl_algobase.h:324:18: error: no match for 'operator=' (operand types are 'boost::basic_string_view<char, std::char_traits<char> >' and 'const char')

        *__result = *__first;

        ~~~~~~~~~~^~~~~~~~~~

In file included from main.cpp:4:0:

/usr/local/include/boost/utility/string_view.hpp:71:26: note: candidate: boost::basic_string_view<charT, traits>& boost::basic_string_view<charT, traits>::operator=(const boost::basic_string_view<charT, traits>&) [with charT = char; traits = std::char_traits<char>]

       basic_string_view& operator=(const basic_string_view &rhs) BOOST_NOEXCEPT {

                          ^~~~~~~~

/usr/local/include/boost/utility/string_view.hpp:71:26: note:   no known conversion for argument 1 from 'const char' to 'const boost::basic_string_view<char, std::char_traits<char> >&'

split

live example

我在这里缺少什么？

Answer 1

通过重载/专门化move_to，您基本上告诉X3如何将boost::iterator_range（实际上只是一对迭代器）转换为boost::string_view。不幸的是，它不知道两者都是“等价的”（一个是另一个的substitute似乎是Spirit中使用的命名法）。因此，您的原始示例有效，因为您明确请求从迭代器到string_view的转换，但是这个失败，因为X3缺少推断相应属性类型所需的信息。

特别是问题似乎是here，在那里测试解析器的属性（在本例中为raw_attribute_type）是否与期望属性的value_type兼容（boost::string_view ）。此测试失败，然后选择未按“原样传递”属性的代码路径，从而导致出现错误。

考虑到所有这些，似乎有两种可能的方法：要么明确地请求转换，要么向Spirit提供有关属性兼容性的信息。

缺少我们在Qi（attr_cast，as[]）中的一些助手，似乎在X3中强制进行属性转换的方法是创建一个具有所需实际类型的额外规则：

x3::rule<class str,boost::string_view> str= x3::raw[ +~char_('_')] >> '_';
auto const str_vec = *str;

您也可以（特别是如果您需要在多个规则中执行此操作）使用我已经看过几次使用的方法（如here）创建一个可以像{{previous question一样使用的变量模板lambda 1}}隐藏了额外规则的创建，并强制as<T>(parser)的属性转换为parser。

T

向Spirit提供有关属性兼容性信息的方法似乎是专门化template<typename T> auto as = [](auto p) { return rule<struct _, T>{} = as_parser(p); }; auto const str_vec = *as<boost::string_view>(x3::raw[ +~char_('_')] >> '_'); ：

x3::traits::is_substitute

但是正如你在评论中提到的那样，这似乎不是一个记录在案的定制点，因此我不确定使用它是否是个好主意。理想情况下，这在X3中默认是专门的，但正如在{{3}}中所评论的那样，迭代器引用的存储必须是连续的这一事实使情况变得复杂。