Getting the ptree from boost::property_tree::ptree::iterator

Question

I have a piece of code that iterates over a boost property tree (XML).
I need a ptree of the current node, not the children of the node.

UPDATE

xml tree

<node id="A.html">
    <subnode> child A1 </subnode>
    <subnode> child A2 </subnode>
</node>

<node id="B.html">
    <subnode> child B1 </subnode>
    <subnode> child B2 </subnode>
</node>

itteration code

void parse_tree(ptree& pt, std::string key)
{
    string nkey;
    if (!key.empty())
    nkey = key + ".";

    ptree::const_iterator end = pt.end();
    for(ptree::iterator it = pt.begin(); it != end; ++it){

        //if the node's id is a .html filname, save the node to file
        string id = it->second.get("<xmlattr>.id","");

        if(id.find("B.html") != std::string::npos){  //Let's just test for "B.html"
            write_xml("test.html", pt);           //saves entire tree
            write_xml("test.html", it->second);   //saves only children of the node
        }

        parse_tree(it->second, nkey + it->first); //recursion
    }
}

Results using write_xml("test.html", pt)

(We get the entire tree, we only want the node)

<node id="A.html">
    <subnode> child A1 </subnode>
    <subnode> child A2 </subnode>
</node>
<node id="B.html">
    <subnode> child B1 </subnode>
    <subnode> child B2 </subnode>
</node>

Results using write_xml("test.html", it->second)

(We have no parent node.. only child nodes)

<subnode> child B1 </subnode>
<subnode> child B2 </subnode>

Desired result

(We want the node, and it's children,.. like so)

<node id="B.html">
    <subnode> child B1 </subnode>
    <subnode> child B2 </subnode>
</node>

sehe · Accepted Answer · 2015-02-06T22:23:01.877

UPDATE 2

Rewritten in response to the comment/updated question.

There are two ways.

You can use the undocumented function write_xml_element to write the single element (using the key as element name):

    // write the single element: (undocumented API)
    boost::property_tree::xml_parser::write_xml_element(
            std::cout, it->first, it->second,
            0, settings
        );

or you can create a new ptree object with the single child

    ptree tmp;
    tmp.add_child(it->first, it->second);
    write_xml(std::cout, tmp, settings);

Live On Coliru

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

#include <fstream>
#include <iostream>

using namespace boost::property_tree;


void parse_tree(ptree& pt, std::string key)
{
    std::string nkey;
    auto settings = xml_parser::xml_writer_make_settings<std::string>('\t', 1);

    if (!key.empty()) {
        nkey = key + ".";
    }

    ptree::const_iterator end = pt.end();
    for(ptree::iterator it = pt.begin(); it != end; ++it)
    {
        //if the node's id an .html filname, save the node to file
        std::string id = it->second.get("<xmlattr>.id","");

        if (id.find(key) != std::string::npos) {
            // write the single element: (undocumented API)
            boost::property_tree::xml_parser::write_xml_element(
                    std::cout, it->first, it->second,
                    0, settings
                );

            // or: create a new pt with the single child
            std::cout << "\n==========================\n\n";
            ptree tmp;
            tmp.add_child(it->first, it->second);
            write_xml(std::cout, tmp, settings);
        }

        parse_tree(it->second, nkey + it->first); //recursion
    }
}

int main() {
    ptree pt;
    read_xml("input.txt", pt);

    parse_tree(pt, "B");
}

Output:

<node id="B.html">
    <subnode> child B1 </subnode>
    <subnode> child B2 </subnode>
</node>

==========================

<?xml version="1.0" encoding="utf-8"?>
<node id="B.html">    
    <subnode> child B1 </subnode>
    <subnode> child B2 </subnode>
</node>

Getting values is not my issue.. I need the pTree of the current itteration.. node.second provides a ptree of the child nodes.. I need the parent ptree of those child nodes... I need something like `boost::property_tree::ptree MyPtree = node.second.get_parent();` or something similar. Thanks — aquawicket, Feb 06 '15 at 19:34
That should have been your question then :) Updated the answer. — sehe, Feb 06 '15 at 20:44
sorry for being so vague.. I've updated to fully show what I'm dealing with. And I thank you very much for your help sehe :) — aquawicket, Feb 06 '15 at 22:03
Ah. So you don't have a problem _gettting_ at the information. You want a way to write a fragment of XML. Let me update the answer — sehe, Feb 06 '15 at 22:14
@aquawicket And done. Next time, be sure to make the question clear, you'll get better answers quicker, not waste anyone's time and perhaps even get upvotes. — sehe, Feb 06 '15 at 22:23

Getting the ptree from boost::property_tree::ptree::iterator

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