Iterating on xml file with boost - c++

Question

I am new with boost and xml and I am trying to scan an xml file and save some specific values.
I read this article and my question is: if the xml contains several <sked>, how do I iterate both of them?
maybe
BOOST_FOREACH ()
BOOST_FOREACH () // nested loop
lets say the given xml file as follow (the purpose is to save both IDs):
<?xml version="1.0"? encoding="utf-8"?>
<arrayOfSked>
<sked>
<ID> 1 </ID>
<version>2</version>
<flight>
<carrier>BA</carrier>
<number>4001</number>
<precision>0.1</precision>
</flight>
<flight cancelled="true">
<carrier>BA</carrier>
<number>4002</number>
<precision>0.2</precision>
</flight>
</sked>
<sked>
<ID> 2 </ID>
<version>2</version>
<flight>
<carrier>BA</carrier>
<number>4001</number>
<precision>0.1</precision>
</flight>
<flight cancelled="true">
<carrier>BA</carrier>
<number>4002</number>
<precision>0.2</precision>
</flight>
</sked>
</arrayOfSked>

Answer 1

Taking some inspiration from this older answer of mine (boost::ptree find? or how to access deep arrays? C++), write a function to visit the tree nodes:
template <typename Tree, typename Out>
Out enumerate_nodes(Tree const& pt, typename Tree::path_type path, Out out) {
if (path.empty())
return out;
if (path.single()) {
auto name = path.reduce();
for (auto& child : pt)
{
if (child.first == name)
*out++ = child.second;
}
} else {
auto head = path.reduce();
for (auto& child : pt) {
if (head == "*" || child.first == head) {
out = enumerate_nodes(child.second, path, out);
}
}
}
return out;
}
Now you can simply read the file:
using boost::property_tree::ptree;
ptree pt;
{
std::ifstream ifs("input.txt");
read_xml(ifs, pt);
}
And collect the flights:
std::vector<std::reference_wrapper<ptree const> > flights;
enumerate_nodes<ptree>(pt, "arrayOfSked.sked.flight", back_inserter(flights));
for (ptree const& flight : flights) {
std::cout << "Canceled:\t" << (flight.get("<xmlattr>.cancelled", false)?"yes":"no") << "\n";
std::cout << "Carrier:\t" << flight.get("carrier", "?") << "\n";
std::cout << "Number:\t" << flight.get("number", 0) << "\n";
std::cout << "Precision:\t" << flight.get("precision", 0.0) << "\n";
std::cout << "------------------------------\n";
}
Which prints:
Canceled: no
Carrier: BA
Number: 4001
Precision: 0.1
------------------------------
Canceled: yes
Carrier: BA
Number: 4002
Precision: 0.2
------------------------------
Canceled: no
Carrier: BA
Number: 4001
Precision: 0.1
------------------------------
Canceled: yes
Carrier: BA
Number: 4002
Precision: 0.2
------------------------------
Full Demo Online
Live On Coliru
#include <boost/property_tree/xml_parser.hpp>
#include <iostream>
template <typename Tree, typename Out>
Out enumerate_nodes(Tree const& pt, typename Tree::path_type path, Out out) {
if (path.empty())
return out;
if (path.single()) {
auto name = path.reduce();
for (auto& child : pt)
{
if (child.first == name)
*out++ = child.second;
}
} else {
auto head = path.reduce();
for (auto& child : pt) {
if (head == "*" || child.first == head) {
out = enumerate_nodes(child.second, path, out);
}
}
}
return out;
}
int main() {
using boost::property_tree::ptree;
ptree pt;
{
std::ifstream ifs("input.txt");
read_xml(ifs, pt);
}
std::vector<std::reference_wrapper<ptree const> > flights;
enumerate_nodes<ptree>(pt, "arrayOfSked.sked.flight", back_inserter(flights));
for (ptree const& flight : flights) {
std::cout << "Canceled:\t" << (flight.get("<xmlattr>.cancelled", false)?"yes":"no") << "\n";
std::cout << "Carrier:\t" << flight.get("carrier", "?") << "\n";
std::cout << "Number:\t" << flight.get("number", 0) << "\n";
std::cout << "Precision:\t" << flight.get("precision", 0.0) << "\n";
std::cout << "------------------------------\n";
}
}