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JSON Array using Boost::Ptree

How to create a boost ptree which can be encoded to below JSON? i.e. I want to know how JSON Array of JSON Objects can be represented in boost ptree..

[
{"3":"SomeValue"},
{"40":"AnotherValue"},
{"23":"SomethingElse"},
{"9":"AnotherOne"},
{"1":"LastOne"}
]

I must say the below link doesn't answer: Creating JSON arrays in Boost using Property Trees

Solution

  • The link does answer it. All the answers clearly show that you should use push_back (or insert, actually), not put_child.

    You also have to read past the "how to make the array" and realize that you cannot have arrays as document root.

    This is a symptom of the fact that Boost Ptree is not a JSON library. It's a Property Tree library, and it supports only property trees. The limitations are documented:

    https://www.boost.org/doc/libs/1_74_0/doc/html/property_tree/parsers.html#property_tree.parsers.json_parser

    enter image description here

    DEMO

    Here's the best you can do, assuming you did not really need the array as document root:

    Live On Coliru

    #define BOOST_BIND_GLOBAL_PLACEHOLDERS 
#include <boost/property_tree/json_parser.hpp>
#include <iostream>

using boost::property_tree::ptree;

int main() {
    ptree arr;

    for (auto [k,v]: { std::pair
            {"3",  "SomeValue"},
            {"40", "AnotherValue"},
            {"23", "SomethingElse"},
            {"9",  "AnotherOne"},
            {"1",  "LastOne"} })
    {
        ptree element;
        element.put(k, v);
        arr.push_back({"", element});
    }

    // can't have array at root of doc...
    ptree doc;
    doc.put_child("arr", arr);
    write_json(std::cout, doc);
}

    Prints

    {
    "arr": [
        {
            "3": "SomeValue"
        },
        {
            "40": "AnotherValue"
        },
        {
            "23": "SomethingElse"
        },
        {
            "9": "AnotherOne"
        },
        {
            "1": "LastOne"
        }
    ]
}