Getting a flatten json to map<string, string>

[amirmasoudabdol]

I'm reading some on the flatten JSON, and I'm wondering what'd be the best way to cast the whole flatten json to a map<string, string>. I'm aware that I can iterate over items, and prepare it manually, but is there any better way?

I'm using C++17, and Apple Clang. I'm using the version 3.7.3.

[nlohmann]

Can you provide an example please?

[amirmasoudabdol]

Now that I'm thinking about it, maybe it's not that straightforward, but this is what I'm trying to do:

    // create JSON value
     json j_flattened =
     {
         {"/answer/everything", 42},
         {"/happy", true},
         {"/list/0", 1},
         {"/list/1", 0},
         {"/list/2", 2},
         {"/name", "Niels"},
         {"/nothing", nullptr},
         {"/object/currency", "USD"},
         {"/object/value", 42.99},
         {"/pi", 3.141}
     };
  
     map<string, string> flatten_json_to_map;

So, I'd like to have the entire j_flattened into the flatten_json_to_map. I see that I need to do a lot of casting, but I'm thinking/asking whether there is an easier solution. I can use the fmt library but then I'll face the same problem of using std::to_string since I have to query the type of each value.

[nlohmann]

No, there is no simple way. In particular, the library provides no built-in conversion from boolean/number/null/etc. to string. You could use dump() for these cases, but you would need to write your own function for this.

Idea (untested):

map<string, string> flatten_json_to_map(const json& j)
{
    map<string, string> result;

    auto flattened_j = j.flatten();

    for (auto entry : flattened_j.items())
    {
        switch (entry.value().type())
        {
            // avoid escaping string value
            case value_t::string:
                result[entry.key()] = entry.value();
                break;

            // use dump() for all other value types
            default:
                result[entry.key()] = entry.value().dump();
                break;
        }
    }

    return result;
}

[amirmasoudabdol]

Your method indeed works and I don't see anything odd, yet. It's what I had in mind too. I'll close the issue and report if I found any bug in it.

Thanks! :-)