Json: [Question] Access multi-level json objects

[SimplyLiz]

Sry for posting a question here, but you don't have a forum and i couldn't figure out how to do this properly.

For my game, i want to store information about sprites in a json file.
First Level - Sprite type (Terrain, Building, Water, ...)
Second Level - Sprite ID (Unique ID to access sprites)
Third Level - Detail Information (Filename, which can vary)

My Implementation:

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

  using json = nlohmann::json;

  void accessTileData(std::string TileType, int tileID);
  json _json;

  int main() {
      // create a JSON object

        _json["terrain"]["0"]["filename"] = std::string("images/floor/floor.png");
        _json["terrain"]["0"]["isPowered"] = true;
        _json["terrain"]["1"]["filename"] = std::string("images/floor/floor2.png");
        _json["terrain"]["1"]["isPowered"] = true;
        _json["terrain"]["2"]["filename"] = std::string("images/floor/floor3.png");
        _json["terrain"]["2"]["isPowered"] = true;
        _json["terrain"]["3"]["filename"] = std::string("images/floor/floor4.png");
        _json["terrain"]["3"]["isPowered"] = true;
        _json["buildings"]["4"]["filename"] = std::string("images/buildings/house1.png");
        _json["buildings"]["4"]["type"] = "building";
        _json["buildings"]["4"]["zone"] = "residential";

        accessTileData("terrain", 2);

  }


  void accessTileData(std::string TileType, int tileID) {
    for (json::iterator it = _json.begin(); it != _json.end(); ++it) {
      if (it.key() == TileType) {
        std::cout << "Terrain Tiles:\n\t" << it.value() << std::endl;            

              // This retrieves more then just the filename value
              std::string retrievedFileName = _json[it.key()][std::to_string(tileID)]["filename"].dump();
              std::cout << "Filename of Tile " << tileID  << std::endl << retrievedFileName;
              // Output:
              // Filename of Tile 2
              // "images/floor/floor3.png"  0  {"filename":"images/floor/floor.png","isPowered":true}


              // this does not work
        for (json::iterator it_meta = it.value().begin(); it_meta != it.value().end(); ++it) {
          std::cout << "\t" << it_meta.key() << "  " << it_meta.value() << std::endl;
        }
              // Error Message
              // prog.exe: ./nlohmann/json.hpp:4087: nlohmann::detail::iter_impl<BasicJsonType>::reference nlohmann::detail::iter_impl<BasicJsonType>::operator*() const [with BasicJsonType = nlohmann::basic_json<>; nlohmann::detail::iter_impl<BasicJsonType>::reference = nlohmann::basic_json<>&]: Assertion `m_it.object_iterator != m_object->m_value.object->end()' failed.
      }
    }
  }

How do i properly retrieve all the informations of a tileID ?
Is there a possibility to retrieve a tile id (second key) from the json object without specifying the first key (type)?

[nlohmann]

I'm not sure what you mean. Maybe this helps, using the items() function:

#include <iostream>
#include "json.hpp"

using json = nlohmann::json;

int main() {
    json _json;
    _json["terrain"]["0"]["filename"] = std::string("images/floor/floor.png");
    _json["terrain"]["0"]["isPowered"] = true;
    _json["terrain"]["1"]["filename"] = std::string("images/floor/floor2.png");
    _json["terrain"]["1"]["isPowered"] = true;
    _json["terrain"]["2"]["filename"] = std::string("images/floor/floor3.png");
    _json["terrain"]["2"]["isPowered"] = true;
    _json["terrain"]["3"]["filename"] = std::string("images/floor/floor4.png");
    _json["terrain"]["3"]["isPowered"] = true;
    _json["buildings"]["4"]["filename"] = std::string("images/buildings/house1.png");
    _json["buildings"]["4"]["type"] = "building";
    _json["buildings"]["4"]["zone"] = "residential";

    // iterate the outer object
    for (auto& i : _json.items())
    {
        // iterate that object's items
        for (auto& j : i.value().items())
        {
            // output the keys
            std::cout << i.key() << " -> " << j.key() << std::endl;
        }
    }
}

Output:

buildings -> 4
terrain -> 0
terrain -> 1
terrain -> 2
terrain -> 3

[SimplyLiz]

Thank you, that's no exactly what i was looking for but it helps!