第二个子节点的XML路径

XML Path to second child

本文关键字：路径 XML 子节点 第二个      更新时间：2023-10-16

我想通过path(不迭代)为ptree中的子节点添加一个新值

为例:

#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
int main() {
  using boost::property_tree::ptree;
  ptree main;
  ptree children;
  children.add("Foo", "bar");
  main.add_child("child", children);
  main.add_child("child", children);
  ptree newChildren("Foo");
  main.put("child{2}.Foo", newChildren.data()); // <-- Access second element?
  // Output
  boost::property_tree::xml_writer_settings<std::string> settings('t', 1);
  boost::property_tree::write_xml(std::cout, main, settings);
  std::cin.ignore();
  return 0;
}

问题是，我不能通过路径访问第二个子节点。有什么格式是有效的吗?

我指的是{2}部分:

"child{2}.Foo"

I tried <2>，[2]，(2)…没有运气…(

我还有希望吗?谢谢你！

我再说一遍:Boost中没有xml解析器/库。

你(ab)使用的是Boost属性树。正如您所发现的，它是一个"属性树"库，这意味着它可以做一些事情。包括写和读属性树。

如果您想要通用的XML内容，请考虑使用XML库(在c++中应该使用哪种XML解析器?)。

废话少说:

Live On Coliru 

#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
int main() {
    using boost::property_tree::ptree;
    ptree pt;
    {
        ptree children; children.add("Foo", "bar");
        pt.add_child("child", children);
        pt.add_child("child", children).put("MARK","so we know it's the second");
    }
    // Output
    boost::property_tree::xml_writer_settings<std::string> settings('t', 1);
    //boost::property_tree::write_xml(std::cout, pt, settings);
    auto child1 = std::find_if(pt.begin(),        pt.end(), [](auto& node) { return node.first == "child"; });
    auto child2 = std::find_if(std::next(child1), pt.end(), [](auto& node) { return node.first == "child"; });
    if (child2 != pt.end())
    {
        boost::property_tree::write_xml(std::cout, child2->second, settings);
        ptree newChildren("Foo");
        child2->second.put("Sub.Foo", newChildren.data()).put("BYE", "ALL DONE"); // <-- Access second element?
        boost::property_tree::write_xml(std::cout << "nnAFTER EDITING:n", child2->second, settings);
    }
}

打印:

<?xml version="1.0" encoding="utf-8"?>
<Foo>bar</Foo>
<MARK>so we know it&apos;s the second</MARK>

AFTER EDITING:
<?xml version="1.0" encoding="utf-8"?>
<Foo>bar</Foo>
<MARK>so we know it&apos;s the second</MARK>
<Sub>
    <Foo>
        Foo
        <BYE>ALL DONE</BYE>
    </Foo>
</Sub>

使用helper函数改进样式:

Live On Coliru

#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
template <typename Tree, typename Out>
Out find_all(Tree& pt, typename Tree::path_type path, Out out) {
    if (path.empty()) {
        *out++ = pt;
        return out;
    }
    auto head = path.reduce();
    for (auto& child : pt)
        if (child.first == head)
            out = find_all(child.second, path, out);
    return out;
}
int main() {
    using boost::property_tree::ptree;
    ptree pt;
    {
        ptree children; children.add("Foo", "bar");
        pt.add_child("child", children);
        pt.add_child("child", children).put("MARK","so we know it's the second");
    }
    // Output
    boost::property_tree::xml_writer_settings<std::string> settings('t', 1);
    //boost::property_tree::write_xml(std::cout, pt, settings);
    std::vector<std::reference_wrapper<ptree> > matches;
    find_all(pt, "child", back_inserter(matches));
    ptree& child2 = matches.at(1);
    child2.put("BYE", "ALL DONE");
    boost::property_tree::write_xml(std::cout, child2, settings);
}

打印

<?xml version="1.0" encoding="utf-8"?>
<Foo>bar</Foo>
<MARK>so we know it&apos;s the second</MARK>
<BYE>ALL DONE</BYE>

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