Boost::property_tree：在 XML 解析器中使用 std::vector<> 在一个键中存储多个值

我的问题与这个问题相关：Boost property_tree：每个键有多个值 https://stackoverflow.com/questions/13072704/boost-property-tree-multiple-values-per-key以及该问题之后的问题：Boost property_tree：模板类上每个键有多个值 https://stackoverflow.com/questions/29801003/boost-property-tree-multiple-values-per-key-on-a-template-class.

我正在尝试解析一个 XML 文件，其中多个值在单个键值处列出，使用std::vector<>。以下代码是我到目前为止所实现的：

#include <boost/optional.hpp>
#include <boost/property_tree/xml_parser.hpp>

namespace boost { namespace property_tree
{

template<typename type>
struct vector_xml_translator
{
    boost::optional<std::vector<type> > get_value(const std::string& str)
    {
        if (!str.empty())
        {
            std::vector<type> values;
            std::stringstream ss(str);

            while (ss)
            {
                type temp_value;
                ss >> temp_value;
                values.push_back(temp_value);
            }

            return boost::optional<std::vector<type> >(values);
        }
        else
        {
            return boost::optional<std::vector<type> >(boost::none);
        }
    }

    boost::optional<std::string> put_value(const std::vector<type>& b)
    {
        std::stringstream ss;
        for (unsigned int i = 0; i < b.size(); i++)
        {
            ss << b[i];
            if (i != b.size()-1)
            {
                ss << " ";
            }
        }
        return boost::optional<std::string>(ss.str());
    }
};

template<typename ch, typename traits, typename alloc, typename data_type>
struct translator_between<std::basic_string<ch, traits, alloc>, std::vector<data_type> >
{
    typedef vector_xml_translator<data_type> type;
};

} // namespace property_tree
} // namespace boost

测试此代码的最小示例如下：

#include <fstream>
#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <XML_Vector_Translator.hpp>


int main()
{
    using boost::property_tree::ptree;

    std::vector<double> test_vector;

    test_vector.push_back(1);
    test_vector.push_back(6);
    test_vector.push_back(3);


    ptree pt;
    pt.add("base", test_vector);

    std::ofstream os("test_file.xml");

    write_xml(os, pt, boost::property_tree::xml_writer_settings<std::string>(' ', 2));

    std::ifstream is("test_file.xml");

    ptree pt_2;
    read_xml(is, pt_2);

    std::vector<int> test_vector_2;

    test_vector_2 = pt_2.get<std::vector<int> >("base");

    for (unsigned int i = 0; i < test_vector_2.size(); i++)
    {
        std::cout << test_vector_2[i] << std::endl;
    }

    return 0;
}

当我运行这段代码时，我收到了许多错误，这使我相信翻译器结构的注册不正确。有人知道如何解决这个问题和/或改进这个代码吗？

1. 正如较旧的答案also指出您必须满足以下要求boost::property_tree::detail::is_translator，所以你需要internal_type / external_type类型定义。

   typedef T internal_type;
   typedef T external_type;
   

2. 接下来，循环错误，需要检查值提取的结果：

   while (ss >> temp_value)
       values.push_back(temp_value);
   

3. 将您自己的类型放入 boost 命名空间中是不好的做法。只有专业化translator_between<>需要在那里。

4. 您可以简化和概括很多代码

全部在一个工作演示中：

Live On Coliru http://coliru.stacked-crooked.com/a/2d31028ff991d28b

#include <boost/optional.hpp>
#include <boost/property_tree/ptree.hpp>
#include <vector>
#include <list>

namespace mylib { namespace xml_translators {

    template<typename T> struct container
    {
        // types
        typedef T internal_type;
        typedef T external_type;

        boost::optional<T> get_value(const std::string& str) const
        {
            if (str.empty())
                return boost::none;

            T values;
            std::stringstream ss(str);

            typename T::value_type temp_value;
            while (ss >> temp_value)
                values.insert(values.end(), temp_value);

            return boost::make_optional(values);
        }

        boost::optional<std::string> put_value(const T& b) {
            std::stringstream ss;
            size_t i = 0;
            for (auto v : b)
                ss << (i++?" ":"") << v;
            return ss.str();
        }
    };

} }

namespace boost { namespace property_tree {
    template<typename ch, typename traits, typename alloc, typename T>
        struct translator_between<std::basic_string<ch, traits, alloc>, std::vector<T> > {
            typedef mylib::xml_translators::container<std::vector<T> > type;
        };

    template<typename ch, typename traits, typename alloc, typename T>
        struct translator_between<std::basic_string<ch, traits, alloc>, std::list<T> > {
            typedef mylib::xml_translators::container<std::list<T> > type;
        };
} }

#include <sstream>
#include <iostream>
#include <boost/property_tree/xml_parser.hpp>

int main()
{
    std::stringstream ss;
    using boost::property_tree::ptree;

    {
        ptree pt;
        pt.add("base", std::vector<double> { 1, 6, 3 });

        write_xml(ss, pt, boost::property_tree::xml_writer_settings<std::string>(' ', 2));
    }

    {
        ptree pt;
        read_xml(ss, pt);

        std::cout << "As string: '" << pt.get("base", "") << "'\n";
        auto roundtrip = pt.get<std::list<int> >("base");
        for (auto i : roundtrip)
            std::cout << i << std::endl;
    }
}

Prints

As string: '1 6 3'
1
6
3

¹ Boost property_tree：每个键有多个值 https://stackoverflow.com/questions/13072704/boost-property-tree-multiple-values-per-key，另请参阅恒等转换器http://www.boost.org/doc/libs/1_64_0/doc/html/boost/property_tree/id_translator.html http://www.boost.org/doc/libs/1_64_0/doc/html/boost/property_tree/id_translator.html