[Help] How to Improve Json Output Performance with Large Json Arrays

[calben]

Hey everyone,

I have class A which includes a std::deque<class B>.
Both A and B have an AsJson() that return a json object, where A's AsJson pushes back many instances of B onto an array, and later on I print this Json as a string.

    nlohmann::json json;
    // add some other fields
    ...
    ...
    for (auto e : events) {
        json["events"].push_back(e->AsJson());
    }
    return json;
    // later outputting json to stream as string or cbor

Constructing the large Json takes a bit of memory and time and then the whole things needs to be processed again to format to a string as well.
Is there a better way to handling constructing and outputting Jsons with large arrays with this library?

Thanks!

[igoloe]

Use an json array and reserve.

nlohmann::json::array_t eventsAsJson;
eventsAsJson.reserve(events.size());

// for-loop or std::for_each

return {"events",std::move(eventsAsJson)};

[nlohmann]

@calben Does @igoloe 's proposal work for you?

[calben]

That does help a bit!
Thank you.