How to parse nested arrays inside json using C++ - c++

Question

I know how to parse "normal" looking JSON data in C++. Usually, I do this, using boost::property_tree and read_json method. It may look like so:
BOOST_FOREAH(ptree::value_type &v, pt.get_child("rows"){
vec.push_back(v.second.get<std::string>("key"));
}
and the code above corresponds to this JSON file:
{
"rows":[{
"key":"1"
},{
"key":"2"
}]
}
However, the Neo4j result-set that I get, looks like:
{
"columns":{...},
"data":[[["object 1"]], [["object 2"]], [["object 3"]]]
}
I'm interested and want to parse "data" node. I tried to do it like so:
BOOST_FOREAH(ptree::value_type &v, pt.get_child("data"){
vec.push_back(v.second.data());
}
but this does not work. I do not get an error, but my vector vec remains empty, or to be more precise it is populated with empty values. So, that when I iterate through this vec I see a number of elements, but they do not have any value. Whereas, I want to have values "object 1", "object 2", "object 3".

Answer 1

The solution looks like this:
using boost::property::ptree;
ptree pt;
//... populate ptree pt with data from some source
BOOST_FOREACH(ptree::value_type &v, pt.get_child('data')){
ptree subtree1 = v.second;
BOOST_FOREACH(ptree::value_type &vs, subtree1){
ptree subtree2 = vs.second;
BOOST_FOREACH(ptree::value_type &vs2, subtree2){
do_something(vs2.second.data());
}
}
}
This code makes it possible to parse such JSON structure:
{
"data":[[["object 1"]], [["object 2"]], [["object 3"]]]
}
So, contrary to what some people are saying, actually, there is no need to use other third-party libraries. Use just boost and you are done.

Answer 2

This is an example of how I do it. You have to know the JSON structure ahead of time.
#include <boost/lexical_cast.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
boost::property_tree::ptree pt, sub_pt;
std::string json_str, key, sub_key;
std::stringstream ss;
int value = 0, bus_num = 0;
json_str = "{\"arduino_1\": {\"bus_1\": 17425,\"bus_2\": 1025,\"bus_3\": 0,\"bus_4\": 0,\"bus_5\": 0,\"bus_6\": 0,\"bus_7\": 0,\"bus_8\": 0}}";
ss << json_str; // put string into stringstream
boost::property_tree::read_json(ss, pt); // put stringstream into property tree
for (boost::property_tree::ptree::iterator iter = pt.begin(); iter != pt.end(); iter++)
{
// get data
key = boost::lexical_cast <std::string>(iter->first.data());
sub_pt = iter->second;
// iterate over subtree
for (boost::property_tree::ptree::iterator sub_iter = sub_pt.begin(); sub_iter != sub_pt.end(); sub_iter++)
{
// get data
sub_key = boost::lexical_cast <std::string>(sub_iter->first.data());
value = boost::lexical_cast <int>(sub_iter->second.data());
}
}