irrlicht/source/lib/json/docs/examples/ordered_json.cpp

#include <iostream>
#include <nlohmann/json.hpp>

using ordered_json = nlohmann::ordered_json;

int main()
{
    ordered_json j;
    j["one"] = 1;
    j["two"] = 2;
    j["three"] = 3;

    std::cout << j.dump(2) << '\n';
}