How to get array from nlohmann json

Question

I tried to search how to get array from json using JSON for Modern C++, but I couldn't find answer.

I have json like this:

{
  "Command": "cmd",
  "Data":{"time": 200, "type":1},
  ...
}

And I want to ask how to get object with key "Data", how to store it and how to access it's elements (count of elements and keys in data can change depending on command).

Thanks for help

Answer 1

You can read a json file into a json object like that:

std::ifstream jsonFile("commands.json");
nlohmann::json commands;
jsonFile >> commands;

To retrieve the "Data" object (and print the number of elements it contains):

nlohmann::json data = commands["Data"];
std::cout << "Number of items in Data: " << data.size() << std::endl;

And finally to loop over all keys and values in "Data":

for (auto it = data.begin(); it != data.end(); ++it)
{
    std::cout << it.key() << ": " << it.value() << std::endl;
}