Boost :: property_tree:使用std :: vector<>在XML解析器中将多个值存储在一个键中 [英] Boost::property_tree: Using std::vector<> in XML parser to store multiple values in one key
问题描述
我的问题与此问题有关: Boost property_tree:每个键有多个值,然后回答该问题:提升property_tree:在模板类上,每个键都有多个值。
My question is related to this question: Boost property_tree: multiple values per key and to a question following that question: Boost property_tree: multiple values per key, on a template class.
我正在尝试解析一个XML文件,该文件中多个值列在使用 std :: vector<>
的单个键值。到目前为止,我已经实现了以下代码:
I am trying to parse an XML file in which multiple values are listed at a single key value using std::vector<>
. The following code is what I have implemented so far:
#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
测试该代码的最小示例如下:
A minimal example to test this code is as follows:
#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,我得到了很多错误,这导致我认为翻译器结构的注册不正确。有人知道如何解决此问题和/或改进此代码吗?
When I run this code I get a number of errors, which lead me to believe that the registration of the translator structure is not right. Does anybody have an idea of how to solve this issue and/or improve this code?
推荐答案
-
正如较早的答案也所指出的那样,您必须满足
boost :: property_tree :: detail :: is_translator
的要求,因此您需要internal_type
/external_type
typedefs。
As the older answer also points out¹ you must satisfy the requirements for
boost::property_tree::detail::is_translator
, so you need theinternal_type
/external_type
typedefs.
typedef T internal_type;
typedef T external_type;
接下来,循环是错误的,您需要检查值提取的结果:
Next up, the loop is wrong, you need check the result of the value extraction:
while (ss >> temp_value)
values.push_back(temp_value);
将自己的类型放在boost名称空间中是一种不好的做法。仅需要 translator_between<>
的专业化即可。
您可以简化和概括很多代码
You can simplify and generalize a lot of the code
全部在工作的演示中:
#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;
}
}
打印
As string: '1 6 3'
1
6
3
¹提升property_tree:每个键有多个值,另请参见身份翻译器 http://www.boost.org/doc/libs/1_64_0/doc/html/boost/property_tree/id_translator.html
¹ Boost property_tree: multiple values per key, see also the identity translator http://www.boost.org/doc/libs/1_64_0/doc/html/boost/property_tree/id_translator.html
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