Parse JSON array value as std::string using Boost

Question

I'm trying to parse a std::string JSON string with this code:

        std::string ss = "{ \"id\" : \"abc123\", \"number\" : \"0123456789\", \"somelist\" : [{ \"timestamp\" : \"May 1, 2015\" , \"data\" : { \"description\" : \"some description\", \"value\" : \"100.000000\" } }] }";

        ptree pt2;
        std::istringstream is(ss);
        read_json(is, pt2);
        std::string _id = pt2.get<std::string>("id");
        std::string _number = pt2.get<std::string>("number");
        std::string _list = pt2.get<std::string>("somelist"); 


        for (auto& e : pt2.get_child("somelist")) {
            std::cout << "timestamp: " << e.second.get<std::string>("timestamp") << "\n";
            for (auto& e1 : pt2.get_child("data")){ // not working
                std::cout << "description: " << e1.second.get<std::string>("description") << "\n";
                std::cout << "value: " << e1.second.get<std::string>("amount") << "\n";
            }
        }

Although my target is not to print the child items (nor convert the JSON string into C++ array). The code above does not work.

I want to know how to get the value of data not as array or something, just as string like this [{ "timestamp" : "May 1, 2015" , "data" : { "description" : "some description", "value" : "100.000000" } }]

Just need the JSON Array as-is as std::string

Have you tried something like std::stringstream ss; write_json(ss, pt2.get_child("data")); ? In your case, .get_child("somelist").get_child("data") or e.get_child("data").. depending where in your code you want to use it. — wendelbsilva
– wendelbsilva, Commented Jul 10, 2015 at 19:47
doing write_json(ss, pt2.get_child("data")); causes no such node error :-) — quarks
– quarks, Commented Jul 10, 2015 at 19:53
Huh? Just tried here and works as a charm. After the printing timestamp and added those lines: ptree d = e.second.get_child("data"); std::stringstream s1; write_json(s1, d); std::cout <<s1.str << std::endl;. Demo Link — wendelbsilva
– wendelbsilva, Commented Jul 10, 2015 at 20:40

Pradhan · Accepted Answer · 2015-07-10 20:45:25Z

1

boost/property_tree/json_parser.hpp implements write_json, which is, as you would expect, the inverse of read_json. Since ptree stores arrays as objects with an empty key, to achieve the representation you want, you would loop over the top-level ptrees in pt2.get_child("somelist"), call write_json on each of them and format these representations as you wish.

for(auto const& node : pt2.get_child("somelist"))
 write_json(std::cout, node.second);

Coliru Demo.

edited Jul 10, 2015 at 20:45

answered Jul 10, 2015 at 20:14

Pradhan

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