RapidJSON/C++: Better ways to create objects/arrays?

Question

I've just begun using RapidJSON; currently, I've got a STL map of strings; and I want to represent it as JSON.

So far, I've done this:

using JSONDocument = rapidjson::GenericDocument<rapidjson::UTF8<>>;
using JSONValue = rapidjson::GenericValue<rapidjson::UTF8<>>;

    JSONDocument jsonRoot(rapidjson::kArrayType);
        for (auto const &kv : localeMap) {
            std::string key = kv.first;
            std::replace(key.begin(), key.end(), ' ','_');
            boost::to_lower(key);
            JSONValue k(rapidjson::kObjectType);
            JSONValue v(rapidjson::kObjectType);
            k.SetString(key,jsonRoot.GetAllocator());
            v.SetString(kv.second,jsonRoot.GetAllocator());

            JSONValue kv_(rapidjson::kObjectType);
            kv_.AddMember(k,v,jsonRoot.GetAllocator());
            jsonRoot.PushBack(kv_, jsonRoot.GetAllocator());
        }

And it works, but that looks terribly clunky to me. I cannot figure out if there's a better/shorter/more performant way of doing this... I've tried several variations of trying to create the object in place but they either don't compile or crash at runtime.

Any hints?

Are you locked into RapidJSON? nlohmann::json makes it [really easy](https://github.com/nlohmann/json#conversion-from-stl-containers) — Shawn, Jul 20 '18 at 00:18
Have you tried [ThorsSerializer](https://github.com/Loki-Astari/ThorsSerializer) You don't need to write any code to serialize a std::map. — Martin York, Jul 23 '18 at 19:19

score 4 · Answer 1 · answered Jul 22 '18 at 07:11

        JSONValue k(rapidjson::kObjectType);
        JSONValue v(rapidjson::kObjectType);
        k.SetString(key,jsonRoot.GetAllocator());
        v.SetString(kv.second,jsonRoot.GetAllocator());

Can be simplified as :

        JSONValue k(key, jsonRoot.GetAllocator());
        JSONValue v(kv.second, jsonRoot.GetAllocator());

For a performance enhancement, you may reserve the size of array type before multiple PushBack():

jsonRoot.Reserve(localMap.size(), jsonRoot.GetAllocator());

And if all you need is a JSON, you may use SAX API (rapidjson::Writer) instead.

RapidJSON/C++: Better ways to create objects/arrays?

1 Answers1