nlohmann::json and =nullptr

[apivovarov]

Can I use operators = nullptr and == nullptr with nlohmann::json?

For example:

nlohmann::json myjson = nullptr;

std::ifstream jsonFile (path);
try {
  jsonFile >> myjson;
} catch (nlohmann::json::exception&) {
  myjson = nullptr;
  cout << "Load json file failed\n";
}

if (myjson == nullptr) {
  cout << "Json is not loaded\n";
}

What exactly json myjson = nullptr is doing?

[dota17]

yes, you can. There are several implements about overload operator= and operator== inside this lib,
if the assigned value or the compared value are JSON type value(nlohmann::json), then it's ok to use it.
json myjson = nullptr is to set myjson to null, no longer hold the original value.

[apivovarov]

Can I use myjson == nullptr to check that nlohmann::json object was created but never filled with data?

if (myjson == nullptr) {
  cout << "Json is not loaded\n";
}

[nlohmann]

Yes, you can. It would be even more expressive if you would use if (myjson.is_null()).

[nlohmann]

More info:

• https://nlohmann.github.io/json/doxygen/classnlohmann_1_1basic__json_a122640e7e2db1814fc7bbb3c122ec76e.html#a122640e7e2db1814fc7bbb3c122ec76e
• https://nlohmann.github.io/json/doxygen/classnlohmann_1_1basic__json_afe9a6fe72337a174cfb117a2081d2cfc.html#afe9a6fe72337a174cfb117a2081d2cfc

[apivovarov]

Thank you!