Getting the ptree from boost::property_tree::ptree::iterator - c++

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>

Answer 1

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>