reading nested json file w/ boost - c++

Question

I'm trying to read a JSON formatted file which is nested with the BOOST library in C++.
I tried a couple of things, browsed through many questions in this forum, but I couldn't find anything really similar, or that would work.
the json file im looking at has the following structure
{
"ABC": {
"FF:[10.0,20.0]": {
"GHG:[-2.5,-2.0]": {
"value": 1.1176470518112183,
"error": 0.013857235087295462
},
"GHG:[1.566,2.0]": {
"value": 0.9958805441856384,
"error": 0.027176504445043704
}
},
"FF:[30.0,50.0]": {
"GHG:[-2.5,-2.0]": {
"value": 1.1176470518112183,
"error": 0.013857235087295462
},
"GHG:[2.0,2.5]": {
"value": 1.0464363098144531,
"error": 0.061588554028766326
}
}
},
"ZXY": {
"FF:[10.0,20.0]": {
"GHG:[-2.5,-2.0]": {
"value": 1.1176470518112183,
"error": 0.013857235087295462
},
"GHG:[1.566,2.0]": {
"value": 0.9958805441856384,
"error": 0.027176504445043704
}
},
"FF:[30.0,50.0]": {
"GHG:[-2.5,-2.0]": {
"value": 1.1176470518112183,
"error": 0.013857235087295462
},
"GHG:[2.0,2.5]": {
"value": 1.0464363098144531,
"error": 0.061588554028766326
}
}
}
}
i was trying to use the BOOST_FOREACH method as is described here:
http://www.ce.unipr.it/people/medici/boost_ptree.html
#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/foreach.hpp>
#include <iostream>
namespace pt = boost::property_tree;
pt::ptree tree;
int main() {
pt::read_json("bla.json", tree);
BOOST_FOREACH( pt::ptree::value_type const&v, tree.get_child("ABC") ) {
const std::string & key = v.first;
const pt::ptree & subtree = v.second;
//const pt::ptree & subsubtree = v.second;
std::cout << key << std::endl;
if(subtree.empty()) {
std::cout << "subtree empty" << std::endl;
} else {
std::cout << "subtree not empty" << std::endl;
BOOST_FOREACH( pt::ptree::value_type const&sv, subtree.get_child(key) ) {
const std::string & subkey = sv.first; // key
const pt::ptree & subsubtree = sv.second; // value (or a subnode)
if(subsubtree.empty()) {
std::cout << "subsubtree empty" << std::endl;
} else {
std::cout << "subsubtree not empty" << std::endl;
std::cout << subsubtree.data() << std::endl;
}
}
}
}
return 0;
}
but i always get an error that there's no such node:
terminate called after throwing an instance of 'boost::wrapexcept<boost::property_tree::ptree_bad_path>'
what(): No such node (FF:[10.0,20.0])
Aborted
i'm pretty sure this is not a hard problem, but i'm kind of a newbie with c++ and i really appreciate any help!

Answer 1

Finally, I got it that your get_child usage is not correct! Just pass the tree to range-based for.
#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/foreach.hpp>
#include <iostream>
namespace pt = boost::property_tree;
pt::ptree tree;
int main() {
pt::read_json("bla.json", tree);
for(auto&& v : tree.get_child("ABC")) {
const std::string & key = v.first; // key
const pt::ptree & subtree = v.second; // value (or a subnode)
//const pt::ptree & subsubtree = v.second; // value (or a subnode)
std::cout << key << std::endl;
if(subtree.empty()) {
// This is a key:value
// use subtree.data() as string value or subtree.get_value<T>()
std::cout << "subtree empty" << std::endl;
} else {
// This is a subtree
// use subtree as child
std::cout << "subtree not empty" << std::endl;
for(auto&& sv : subtree/*.get_child(pt::path(key, '\0'))*/) {
[[maybe_unused]]const std::string & subkey = sv.first; // key
const pt::ptree & subsubtree = sv.second; // value (or a subnode)
std::cout << subkey << std::endl;
if(subsubtree.empty()) {
std::cout << "subsubtree empty" << std::endl;
} else {
std::cout << "subsubtree not empty" << std::endl;
std::cout << subsubtree.data() << std::endl;
for(auto&& ssv: subsubtree) {
[[maybe_unused]]const std::string & subsubkey = ssv.first; // key
const pt::ptree & subsubsubtree = ssv.second; // value (or a subnode)
std::cout << subsubkey << std::endl;
if(subsubsubtree.empty()) {
std::cout << "subsubsubtree empty" << std::endl;
if (auto subsubsubtree_v = subsubsubtree.get_value_optional<double>()) {
std::cout << subsubsubtree_v.get() << std::endl;
}
}
else {
std::cout << "subsubtree not empty" << std::endl;
std::cout << subsubtree.data() << std::endl;
}
}
}
}
}
}
return 0;
}
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