Boost filesystem library operating system file

#include<boost/optional.hpp>
#include<boost/filesystem.hpp>
#include<boost/filesystem/fstream.hpp>
#include<boost/optional.hpp>
#include<boost/xpressive/xpressive_dynamic.hpp>
#include<boost/algorithm/string.hpp>
#include<string>
#include<iostream>
using namespace std;
using namespace boost;
using namespace boost::filesystem;
using namespace boost::xpressive;
typedef recursive_directory_iterator  rd_iterator;
//判断特定目录下是否有指定文件
optional<path> find_file(const path& dir, const string& filename) {
    typedef optional<path> result_type;
    if (!exists(dir) || !is_directory(dir)) {
        return result_type();
    }

    rd_iterator end;
    for (rd_iterator pos(dir); pos != end; ++pos) {
        if (!is_directory(*pos) && pos->path().filename() == filename)
        {
            return result_type(pos->path());
        }
    }
    return result_type();
 }


//实现模糊查找文件
void find_files(const path& dir, const string& filename, vector<path>& v) {
    static xpressive::sregex_compiler rc;
    if (!rc[filename].regex_id())
    {
        string str = replace_all_copy(
            replace_all_copy(filename, ".", "\\."),
            "*", ".*"
        );
        rc[filename] = rc.compile(str);
    }
    typedef vector<path> result_type;
    if (!exists(dir) || !is_directory(dir)) {
        return;
    }

    rd_iterator end;
    for (rd_iterator pos(dir); pos != end; ++pos) {
        if (!is_directory(*pos) &&
            regex_match(pos->path().filename(), rc[filename])) {
            v.push_back(pos->path());
        }
    }
}







int main()
{
    optional<path> r = find_file("G:/Reading/papers", "1707.06742.pdf");
    if (r) {
        cout << *r << endl;
    }
    else {
        cout << "file not found" << endl;
    }
    return 0;
}