CODEWITHSUNDEEP
c++arraysjsonnlohmann-json
joe
joe

Reputation: 113

Output Json Array in cpp using nlohmann

I created json objects using nlohmann library with this code:

nlohmann::json dataJson;
auto data = dataJson.array();

data[0]["message"] = "String";
data[0]["timestamp"] = 123;

The output is

{"message":"String", "timestamp": 123}

but i want the output to be

[{"message":"String", "timestamp": 123}]

in an array in order to have the ability to have multiple messages.

So i want to ask what is the best way to add the values in the array, because when I print it, the ouput of the array is null.

I am new at cpp so I want to apologize for the question if is considered too easy, but any help would be appreciated.

Upvotes: 1

Views: 4246

Answers (1)

Richard Hodges
Richard Hodges

Reputation: 69912

nlohmann_json is a very useful library but it does have a few quirks. I find it's best to be explicit about intent.

Lambdas can be very useful here:

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

int main() {

  auto make_object = []
  {
    auto result = nlohmann::json::object();
    result["message"] = "String";
    result["timestamp"] = 123;
    return result;
  };

  auto make_array = [&make_object]
  {
    auto result = nlohmann::json::array();
    result.push_back(make_object());
    return result;
  };

  auto data = make_array();
  std::cout << data.dump() << std::endl;

  return 0;
}

expected output:

[{"message":"String","timestamp":123}]

Upvotes: 4

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