The DataTree object

DataTree object

The DataTree object is the root of a boost' propety_tree. Through the DataTree object, you can generate Data objects which provide tools to access and edit the tree's contents.

The root branch itself can be accessed as a Data object by using the as_data() method:

DataTree datatree;
Data root = datatree.as_data();

Data object

The DataTree::operator[] method returns an object of type Data. The Data object provides several methods to access the content of a DataTree:

Data user_data = datatree["user"];
std::string firstname, lastname;
std::vector<std::string> friends;
unsigned short age;

if (user_data["firstname"].exists())
  firstname = user_data["firstname"].as<std::string>();

if (user_data["lastname"].is_blank())
  throw "user.lastname is an empty string";

if (user_data["friends"].is_array())
  friends = user_data["friends"].to_vector<std::string>();

age = user_data["age"].defaults_to<unsigned short>(21);

It also provides methods to store content in the DataTree:

Data user_data = datatree["user"];

// storing values with the operator= overload
user_data["firstname"] = "Luc";
user_data["age"] = 50;

// storing arrays with the from_vector method
std::vector<std::string> friends = { "roger", "robert", "bernard" };
user_data["friends"].from_vector<std::string>(friends);

Populating a DataTree

You may load a DataTree directly from a json string, stringstream, or by loading a file. Here are a few examples:

  DataTree json_file;

  // From a string
  json_file.from_json("{ \"user\": { \"lastname\": \"Dupuis\" } }");
  std::cout << "User's lastname: " << json_file["user"]["lastname"].as<std::string>() << std::endl;
  json_file.clear(); // The clear method resets the DataTree

  // From a file
  json_file.from_json_file("/tmp/some_file.json");
  std::cout << "File content: " << json_file.to_json() << std::endl;