将boost范围适配器与目录迭代器范围一起使用(Using boost range adaptors with a directory iterator range)

 编辑：我根据乔纳森的回答在我的问题下面添加了一些解决方案 
 
 我想在给定的目录中有一个具有特定名称模式的常规文件列表。 我从boost.filesystem （boost 1.53）中提取了一个例子并对其进行了修改。 这是我基本想要的工作版本： 
 
#include <iostream>
#include <boost/filesystem.hpp>
#include <boost/foreach.hpp>

using namespace std;
using namespace boost::filesystem;

int main(int argc, char* argv[])
{
  path p ("."); // search directory

  try
  {
    if (exists(p))
    {
      if (is_directory(p))
      {
        cout << "logfiles in " << absolute(p) << '\n';
      // I want to replace this part:
        std::list<directory_entry> datFiles;
        for(directory_iterator it(p); it != directory_iterator(); ++it)
        {
          if (is_regular_file(*it) && (extension(*it) == ".dat"))
          {
            datFiles.push_back(*it);
          }
        }
      // part to be replaced ends here
        BOOST_FOREACH(const directory_entry& de, datFiles)
        {
          cout << de << '\n';
        }
      }
    }
  }

  catch (const filesystem_error& ex)
  {
    cout << ex.what() << '\n';
  }

  return 0;
}
 
 这会将所有以.dat结尾的文件的条目附加到目录条目列表中。 我稍后需要更多模式匹配。 然后我尝试用范围做同样的事情，但都失败了。 我现在将任务简化为只复制也不能编译的所有目录条目： 
 
    // replacement starts here
        std::list<directory_entry> datFiles;
        boost::iterator_range<directory_iterator> rng(directory_iterator(p), directory_iterator());should be
        boost::copy(rng, datFiles.begin());
    // replacement ends here
 
 我这样写，因为（来自boost.filesystem的tut3.cpp） 
 
 
 
 directory_iterator :: value_type是directory_entry 
 
 
 因此，该副本可以遍历该范围，获取条目并将它们存储在我的列表中。 但是，我收到了很多来自gcc的错误消息： 
 
In file included from boost_1_53_0/boost/type_traits/decay.hpp:18:0,
                 from boost_1_53_0/boost/filesystem/path_traits.hpp:22,
                 from boost_1_53_0/boost/filesystem/path.hpp:25,
                 from boost_1_53_0/boost/filesystem.hpp:16,
                 from ~/20130519_searchDatFiles/main.cpp:3:
boost_1_53_0/boost/mpl/eval_if.hpp: In instantiation of ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>, boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >’:
boost_1_53_0/boost/range/iterator.hpp:63:63:   instantiated from ‘boost::range_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>’
boost_1_53_0/boost/range/concepts.hpp:256:72:   instantiated from ‘boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>’
boost_1_53_0/boost/concept/detail/has_constraints.hpp:42:5:   instantiated from ‘const bool boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >::value’
boost_1_53_0/boost/concept/detail/has_constraints.hpp:45:31:   instantiated from ‘boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >’
boost_1_53_0/boost/mpl/if.hpp:67:11:   instantiated from ‘boost::mpl::if_<boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >, boost::concepts::constraint<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >, boost::concepts::requirement<boost::concepts::failed************ boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>::************> >’
boost_1_53_0/boost/concept/detail/general.hpp:50:8:   instantiated from ‘boost::concepts::requirement_<void (*)(boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>)>’
boost_1_53_0/boost/range/algorithm/copy.hpp:33:1:   instantiated from ‘OutputIterator boost::range::copy(const SinglePassRange&, OutputIterator) [with SinglePassRange = boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()), OutputIterator = std::_List_iterator<boost::filesystem::directory_entry>]’
~/20130519_searchDatFiles/main.cpp:45:42:   instantiated from here
boost_1_53_0/boost/mpl/eval_if.hpp:60:31: error: no type named ‘type’ in ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>, boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >::f_ {aka struct boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>}’
In file included from boost_1_53_0/boost/range/algorithm.hpp:53:0,
                 from ~/20130519_searchDatFiles/main.cpp:7:
boost_1_53_0/boost/range/algorithm/copy.hpp: In function ‘OutputIterator boost::range::copy(const SinglePassRange&, OutputIterator) [with SinglePassRange = boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()), OutputIterator = std::_List_iterator<boost::filesystem::directory_entry>]’:
~/20130519_searchDatFiles/main.cpp:45:42:   instantiated from here
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: error: no matching function for call to ‘begin(boost::iterator_range<boost::filesystem::directory_iterator> (&)(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()))’
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: note: candidates are:
boost_1_53_0/boost/range/begin.hpp:101:55: note: template<class T> typename boost::range_iterator::type boost::range_adl_barrier::begin(T&)
boost_1_53_0/boost/range/begin.hpp:112:61: note: template<class T> typename boost::range_iterator<const T>::type boost::range_adl_barrier::begin(const T&)
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: error: no matching function for call to ‘end(boost::iterator_range<boost::filesystem::directory_iterator> (&)(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()))’
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: note: candidates are:
boost_1_53_0/boost/range/end.hpp:95:55: note: template<class T> typename boost::range_iterator::type boost::range_adl_barrier::end(T&)
boost_1_53_0/boost/range/end.hpp:106:61: note: template<class T> typename boost::range_iterator<const T>::type boost::range_adl_barrier::end(const T&)
boost_1_53_0/boost/range/algorithm/copy.hpp:35:1: warning: control reaches end of non-void function [-Wreturn-type]
 
 我真的不能过滤出相关的行，但我认为可以使用范围适配器来过滤文件（毕竟，我不只是想复制范围）。 我的印象是，在某种程度上datFiles.begin()不符合复制算法所需的概念。 
 
 
 我的一些解决方案 
 
 基于乔纳森的回答，下面是我提出的一些解决方案（包括过滤）。 
 
 使用全局谓词函数bool isDatFile(const path& p) ： 
 
std::list<directory_entry> datFiles;
boost::copy(rng | boost::adaptors::filtered(isDatFile), std::back_inserter(datFiles));
 
 尽管如此，我更喜欢本地功能，所以我尝试过。 这一个只是检查目录条目是否是一个常规文件，因为is_regular_file过载而需要静态is_regular_file ： 
 
std::list<directory_entry> datFiles;
boost::copy(rng
            | boost::adaptors::filtered(static_cast<bool (*)(const path&)>(&is_regular_file)),
            std::back_inserter(datFiles));
 
 检查范围适配器中的右侧扩展也有点困难，所以我添加了一个本地函数： 
 
std::list<directory_entry> datFiles;
bool BOOST_LOCAL_FUNCTION(const path& p)
{
  return (is_regular_file(p) && (extension(p) == string(".dat")));
} BOOST_LOCAL_FUNCTION_NAME(isDatFile_l)
boost::copy(rng
            | boost::adaptors::filtered(isDatFile_l),
            std::back_inserter(datFiles));
 
 最后，使用绑定的“单线程”： 
 
std::list<directory_entry> datFiles;
boost::copy(rng
            | boost::adaptors::filtered(static_cast<bool (*)(const path&)>(&is_regular_file))
            | boost::adaptors::filtered(boost::bind(std::equal_to<path>(), boost::bind(extension, _1), path(".dat"))),
            std::back_inserter(datFiles));

Edit: I added some solutions below my question, based on Jonathan's answer
 
I want to have a list of regular files with a certain name pattern in a given directory. I took one of the examples from boost.filesystem (boost 1.53) and modified it. Here is a working version of what I basically want:
 
#include <iostream>
#include <boost/filesystem.hpp>
#include <boost/foreach.hpp>

using namespace std;
using namespace boost::filesystem;

int main(int argc, char* argv[])
{
  path p ("."); // search directory

  try
  {
    if (exists(p))
    {
      if (is_directory(p))
      {
        cout << "logfiles in " << absolute(p) << '\n';
      // I want to replace this part:
        std::list<directory_entry> datFiles;
        for(directory_iterator it(p); it != directory_iterator(); ++it)
        {
          if (is_regular_file(*it) && (extension(*it) == ".dat"))
          {
            datFiles.push_back(*it);
          }
        }
      // part to be replaced ends here
        BOOST_FOREACH(const directory_entry& de, datFiles)
        {
          cout << de << '\n';
        }
      }
    }
  }

  catch (const filesystem_error& ex)
  {
    cout << ex.what() << '\n';
  }

  return 0;
}
 
This appends the entry of all files ending with .dat to the list of directory entries. I need more pattern matching later. I then tried to do the same thing with ranges, and failed. I now reduced the task to simply copying all directory entries which also doesn't compile:
 
    // replacement starts here
        std::list<directory_entry> datFiles;
        boost::iterator_range<directory_iterator> rng(directory_iterator(p), directory_iterator());should be
        boost::copy(rng, datFiles.begin());
    // replacement ends here
 
I wrote it this way because (tut3.cpp from boost.filesystem)
 
 
 
directory_iterator::value_type is directory_entry
 
 
So that copy can iterate over the range, get entries and store them in my list. However, I'm getting lots of error messages from gcc:
 
In file included from boost_1_53_0/boost/type_traits/decay.hpp:18:0,
                 from boost_1_53_0/boost/filesystem/path_traits.hpp:22,
                 from boost_1_53_0/boost/filesystem/path.hpp:25,
                 from boost_1_53_0/boost/filesystem.hpp:16,
                 from ~/20130519_searchDatFiles/main.cpp:3:
boost_1_53_0/boost/mpl/eval_if.hpp: In instantiation of ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>, boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >’:
boost_1_53_0/boost/range/iterator.hpp:63:63:   instantiated from ‘boost::range_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>’
boost_1_53_0/boost/range/concepts.hpp:256:72:   instantiated from ‘boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>’
boost_1_53_0/boost/concept/detail/has_constraints.hpp:42:5:   instantiated from ‘const bool boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >::value’
boost_1_53_0/boost/concept/detail/has_constraints.hpp:45:31:   instantiated from ‘boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >’
boost_1_53_0/boost/mpl/if.hpp:67:11:   instantiated from ‘boost::mpl::if_<boost::concepts::not_satisfied<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >, boost::concepts::constraint<boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >, boost::concepts::requirement<boost::concepts::failed************ boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>::************> >’
boost_1_53_0/boost/concept/detail/general.hpp:50:8:   instantiated from ‘boost::concepts::requirement_<void (*)(boost::SinglePassRangeConcept<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>)>’
boost_1_53_0/boost/range/algorithm/copy.hpp:33:1:   instantiated from ‘OutputIterator boost::range::copy(const SinglePassRange&, OutputIterator) [with SinglePassRange = boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()), OutputIterator = std::_List_iterator<boost::filesystem::directory_entry>]’
~/20130519_searchDatFiles/main.cpp:45:42:   instantiated from here
boost_1_53_0/boost/mpl/eval_if.hpp:60:31: error: no type named ‘type’ in ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>, boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())> >::f_ {aka struct boost::range_mutable_iterator<boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)())>}’
In file included from boost_1_53_0/boost/range/algorithm.hpp:53:0,
                 from ~/20130519_searchDatFiles/main.cpp:7:
boost_1_53_0/boost/range/algorithm/copy.hpp: In function ‘OutputIterator boost::range::copy(const SinglePassRange&, OutputIterator) [with SinglePassRange = boost::iterator_range<boost::filesystem::directory_iterator>(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()), OutputIterator = std::_List_iterator<boost::filesystem::directory_entry>]’:
~/20130519_searchDatFiles/main.cpp:45:42:   instantiated from here
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: error: no matching function for call to ‘begin(boost::iterator_range<boost::filesystem::directory_iterator> (&)(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()))’
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: note: candidates are:
boost_1_53_0/boost/range/begin.hpp:101:55: note: template<class T> typename boost::range_iterator::type boost::range_adl_barrier::begin(T&)
boost_1_53_0/boost/range/begin.hpp:112:61: note: template<class T> typename boost::range_iterator<const T>::type boost::range_adl_barrier::begin(const T&)
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: error: no matching function for call to ‘end(boost::iterator_range<boost::filesystem::directory_iterator> (&)(boost::filesystem::directory_iterator, boost::filesystem::directory_iterator (*)()))’
boost_1_53_0/boost/range/algorithm/copy.hpp:34:59: note: candidates are:
boost_1_53_0/boost/range/end.hpp:95:55: note: template<class T> typename boost::range_iterator::type boost::range_adl_barrier::end(T&)
boost_1_53_0/boost/range/end.hpp:106:61: note: template<class T> typename boost::range_iterator<const T>::type boost::range_adl_barrier::end(const T&)
boost_1_53_0/boost/range/algorithm/copy.hpp:35:1: warning: control reaches end of non-void function [-Wreturn-type]
 
I wasn't really able to filter out the relevant lines, but I think that it is possible to filter files using range adaptors (I don't just want to copy the range, after all). My impression is that somewhere along the way datFiles.begin() doesn't satisfy a concept needed by the copy algorithm.
 
 
Some of my solutions
 
Here are some of the solutions (including filtering) I came up with, based on Jonathan's answer.
 
Using a global predicate function bool isDatFile(const path& p):
 
std::list<directory_entry> datFiles;
boost::copy(rng | boost::adaptors::filtered(isDatFile), std::back_inserter(datFiles));
 
I preferred a local function, though, so I tried that. This one is just checking if the directory entry is a regular file, the static cast was needed because is_regular_file is overloaded:
 
std::list<directory_entry> datFiles;
boost::copy(rng
            | boost::adaptors::filtered(static_cast<bool (*)(const path&)>(&is_regular_file)),
            std::back_inserter(datFiles));
 
Checking for the right extension in the range adaptor as well was a bit hard, so I added a local function:
 
std::list<directory_entry> datFiles;
bool BOOST_LOCAL_FUNCTION(const path& p)
{
  return (is_regular_file(p) && (extension(p) == string(".dat")));
} BOOST_LOCAL_FUNCTION_NAME(isDatFile_l)
boost::copy(rng
            | boost::adaptors::filtered(isDatFile_l),
            std::back_inserter(datFiles));
 
And finally the "one-liner" using bind:
 
std::list<directory_entry> datFiles;
boost::copy(rng
            | boost::adaptors::filtered(static_cast<bool (*)(const path&)>(&is_regular_file))
            | boost::adaptors::filtered(boost::bind(std::equal_to<path>(), boost::bind(extension, _1), path(".dat"))),
            std::back_inserter(datFiles));

原文：https://stackoverflow.com/questions/16639666