Jsoncpp - How do I read an array?

Question

I'm stuck at trying to read an array from a Json file.

Here is the People.json file:

{
  "ID": [
    {
      "1": {
        "name": "Fred",
        "favouriteFood": "Cheese",
        "gender": "Male"
      }
    },
    {
      "2": {
        "name": "Bob",
        "favouriteFood": "Cake",
        "gender": "Male"
      }
    }
  ]
}

Here is the function that should read it:

Person choosePerson(int ID)
{
    Person Person;
    ifstream file("People.json");
    Json::Value root;
    Json::Reader reader;
    Json::FastWriter fastWriter;

    reader.parse(file, root);
    Person.id = ID;
    Person.name = fastWriter.write(root["data"][to_string(ID)]["name"]);
    Person.favFood = fastWriter.write(root["data"][to_string(ID)]["favouriteFood"]);
    Person.gender = fastWriter.write(root["data"][to_string(ID)]["gender"]);
    return Person;
}

After Running it I get a "Json::LogicError" exception.

Answer 1

Problem is your JSon which is badly designed. It is bad since objects have keys of unexpected values. Those "1" and "2" make things complicated.

I do not see in documentation how to get list of keys of a JSon object.
Ok I've found getMemberNames(), but you try use it yourself. IMO it would be better to fix this JSon.

So after fixing JSon like this:

{
  "ID":[
    {
      "id":"1",
      "name":"Fred",
      "favouriteFood":"Cheese",
      "gender":"Male"
    },
    {
      "id":"2",
      "name":"Bob",
      "favouriteFood":"Cake",
      "gender":"Male"
    }
  ]
}

Reading of it can look like this:

struct Person {
    std::string id;
    std::string name;
    std::string favouriteFood;
    std::string gender;
};

Person personFromJSon(const Json::Value& json)
{
    return {
        json["id"].asString(),
        json["name"].asString(),
        json["favouriteFood"].asString(),
        json["gender"].asString()
    };
}

std::vector<Person> personsFromJSon(const Json::Value& json)
{
    if (!json.isArray()) return {};
    std::vector<Person> result;
    result.reserve(json.size());
    std::transform(json.begin(), json.end(), std::back_inserter(result), personFromJSon);
    return result;
}

std::vector<Person> personsFromJSon(std::istream& in)
{
    Json::Value root;
    Json::Reader reader;
    reader.parse(in, root);
    return personsFromJSon(root["ID"]);
}

Here is live demo.