Serializing and deserializing JSON with Boost

Question

I'm newbie to C++. What's the easiest way to serialize and deserialize data of type std::Map using boost. I've found some examples with using PropertyTree but they are obscure for me.

Answer 1

Note that property_tree interprets the keys as paths, e.g. putting the pair "a.b"="z" will create an {"a":{"b":"z"}} JSON, not an {"a.b":"z"}. Otherwise, using property_tree is trivial. Here is a little example.

#include <sstream>
#include <map>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;

void example() {
  // Write json.
  ptree pt;
  pt.put ("foo", "bar");
  std::ostringstream buf; 
  write_json (buf, pt, false);
  std::string json = buf.str(); // {"foo":"bar"}

  // Read json.
  ptree pt2;
  std::istringstream is (json);
  read_json (is, pt2);
  std::string foo = pt2.get<std::string> ("foo");
}

std::string map2json (const std::map<std::string, std::string>& map) {
  ptree pt; 
  for (auto& entry: map) 
      pt.put (entry.first, entry.second);
  std::ostringstream buf; 
  write_json (buf, pt, false); 
  return buf.str();
}

Answer 2

Boost versions 1.75 and later now have a robust native JSON library:

https://www.boost.org/doc/libs/develop/libs/json/doc/html/index.html

I don't suggest using Boost.PropertyTree's JSON algorithms anymore, as they are not fully compliant with the spec.