c++ - Mpl for_each 与 mpl 列表

Question

我正在尝试在 for_each 中使用 mpl_list

#include <boost/mpl/list.hpp>
#include <algorithm>
#include <boost/mpl/for_each.hpp>
#include <string>
#include <istream>
#include <ostream>
#include <sstream>
#include <iostream>
#include <boost/mpl/range_c.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/mpl/vector_c.hpp>
#include <boost/mpl/at.hpp>
#include <boost/mpl/placeholders.hpp>
#include <boost/bind.hpp>


using namespace std;

namespace mpl = boost::mpl;


typedef mpl::range_c<char,1,5> range5;
typedef mpl::list<
mpl::int_<1>
, mpl::int_<5>
, mpl::int_<31>
, mpl::int_<14>
, mpl::int_<51>
>  inp_type;

typedef mpl::list<
mpl::int_<1>
, mpl::int_<5>
, mpl::int_<31>
, mpl::int_<14>
, mpl::int_<51>
>  out_type;


template <class T> struct id {};
struct do_this_wrapper {
    static char stat_c ;
    typedef void result_type;

    template<typename U> inline void operator()(int i, U )
    {
        if (i == U::value)
        {
            do_this_wrapper::stat_c = mpl::at_c<out_type,U::value>::type::value;
        }
    }
};


char do_this_wrapper::stat_c ;


int main()
{

    int x;
    std::cin>>x;
    boost::mpl::for_each<inp_type>(boost::bind(do_this_wrapper(), x, _1));

    return do_this_wrapper::stat_c;
};

我有这些错误

*... /usr/include/boost/mpl/list/aux_/iterator.hpp: In instantiation of ‘struct boost::mpl::deref >’: /usr/include/boost/mpl/aux_/at_impl.hpp:37:45: required from ‘struct boost::mpl::at_impl::apply, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >, mpl_::long_<5l> >’ /usr/include/boost/mpl/at.hpp:42:8: required from ‘struct boost::mpl::at_c, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >, 5l>’ ../src/TestProj3.cpp:2664:41: required from ‘void do_this_wrapper::operator()(int, U) [with U = mpl_::int_<5>]’ /usr/include/boost/bind/bind.hpp:313:34: required from ‘void boost::_bi::list2::operator()(boost::_bi::type, F&, A&, int) [with F = do_this_wrapper; A = boost::_bi::list1&>; A1 = boost::_bi::value; A2 = boost::arg<1>]’ /usr/include/boost/bind/bind_template.hpp:32:59: required from ‘boost::_bi::bind_t::result_type boost::_bi::bind_t::operator()(A1&) [with A1 = mpl_::int_<5>; R = boost::_bi::unspecified; F = do_this_wrapper; L = boost::_bi::list2, boost::arg<1> >; boost::_bi::bind_t::result_type = void]’ /usr/include/boost/mpl/for_each.hpp:75:25: required from ‘static void boost::mpl::aux::for_each_impl::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::l_iter, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> > >; LastIterator = boost::mpl::l_iter; TransformFunc = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:79:111: required from ‘static void boost::mpl::aux::for_each_impl::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::l_iter, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> > >; LastIterator = boost::mpl::l_iter; TransformFunc = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:101:97: required from ‘void boost::mpl::for_each(F, Sequence*, TransformOp*) [with Sequence = boost::mpl::list, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >; TransformOp = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:111:38: required from ‘void boost::mpl::for_each(F, Sequence*) [with Sequence = boost::mpl::list, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >; F = boost::_bi::bind_t, boost::arg<1> > >]’ ../src/TestProj3.cpp:2678:77: required from here /usr/include/boost/mpl/list/aux_/iterator.hpp:39:33: error: no type named ‘item’ in ‘struct boost::mpl::l_end’ typedef typename Node::item type; ^ /usr/include/boost/mpl/list/aux_/iterator.hpp: In instantiation of ‘struct boost::mpl::next >’: /usr/include/boost/mpl/aux_/preprocessed/gcc/advance_forward.hpp:68:44: required from ‘struct boost::mpl::aux::advance_forward<4l>::apply
 /usr/include/boost/mpl/aux_/preprocessed/gcc/apply_wrap.hpp:36:8:
                required from ‘struct boost::mpl::apply_wrap1, boost::mpl::l_iter > > >’ /usr/include/boost/mpl/aux_/preprocessed/gcc/advance_forward.hpp:83:21: required from ‘struct boost::mpl::aux::advance_forward<27l>::apply ’ /usr/include/boost/mpl/aux_/preprocessed/gcc/apply_wrap.hpp:36:8:
                required from ‘struct boost::mpl::apply_wrap1, boost::mpl::l_iter > > >’ /usr/include/boost/mpl/aux_/preprocessed/gcc/advance_forward.hpp:92:21: required from ‘struct boost::mpl::aux::advance_forward<31l>::apply, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> > > >’ /usr/include/boost/mpl/aux_/preprocessed/gcc/apply_wrap.hpp:36:8: [ skipping 7 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ] /usr/include/boost/bind/bind_template.hpp:32:59: required from ‘boost::_bi::bind_t::result_type boost::_bi::bind_t::operator()(A1&) [with A1 = mpl_::int_<31>; R = boost::_bi::unspecified; F = do_this_wrapper; L = boost::_bi::list2, boost::arg<1> >; boost::_bi::bind_t::result_type = void]’ /usr/include/boost/mpl/for_each.hpp:79:111: recursively required from ‘static void boost::mpl::aux::for_each_impl::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::l_iter, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> > >; LastIterator = boost::mpl::l_iter; TransformFunc = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:79:111: required from ‘static void boost::mpl::aux::for_each_impl::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::l_iter, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> > >; LastIterator = boost::mpl::l_iter; TransformFunc = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:101:97: required from ‘void boost::mpl::for_each(F, Sequence*, TransformOp*) [with Sequence = boost::mpl::list, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >; TransformOp = boost::mpl::identity; F = boost::_bi::bind_t, boost::arg<1> > >]’ /usr/include/boost/mpl/for_each.hpp:111:38: required from ‘void boost::mpl::for_each(F, Sequence*) [with Sequence = boost::mpl::list, mpl_::int_<5>, mpl_::int_<31>, mpl_::int_<14>, mpl_::int_<51> >; F = boost::_bi::bind_t, boost::arg<1> > >]’ ../src/TestProj3.cpp:2678:77: required from here /usr/include/boost/mpl/list/aux_/iterator.hpp:45:43: error: no type named ‘next’ in ‘struct boost::mpl::l_end*’

如有详细说明或阅读，将不胜感激。提前致谢

Answer 1

问题是

do_this_wrapper::stat_c = mpl::at_c<out_type,U::value>::type::value;

这是要求 MPL 在 out_type 中的位置找到元素对应于 U 的值.自 inp_type值为 51 (除其他事项外)，无法返回 out_type 中位置 51 的元素。 ，因为它只包含 5 个元素。

就我个人而言，我会尝试将这两个序列连接成一个关联序列 ( mpl::map )，然后在其上使用 for_each。