text: The Firebase Realtime Database stores and synchronizes data using a NoSQL cloud database. Data is synchronized across all clients in realtime, and remains available when your app goes offline.
  Before You Begin
  Before you can use Firebase Realtime Database, you need to:
  Register your C++ project and configure it to use Firebase.
  If your C++ project already uses Firebase, then it's already registered and configured for Firebase.
  Add the Firebase C++ SDK to your C++ project.
  Note that adding Firebase to your C++ project involves tasks both in the Firebase console and in your open C++ project (for example, you download Firebase config files from the console, then move them into your C++ project).
  Create a Database
  Navigate to the Realtime Database section of the Firebase console. You'll be prompted to select an existing Firebase project. Follow the database creation workflow.
  Select a starting mode for your Firebase Security Rules:
  - Test mode
  Good for getting started with the mobile and web client libraries, but allows anyone to read and overwrite your data. After testing, make sure to review the Understand Firebase Realtime Database Rules section.
  To get started with the web, Apple, or Android SDK, select testmode.
  - Locked mode
  Denies all reads and writes from mobile and web clients. Your authenticated application servers can still access your database.
  Choose a location for the database.
  Depending on the location of the database, the URL for the new database will be in one of the following forms:
  (for databases inDATABASE_NAME.firebaseio.com
  ) (for databases in all other locations)DATABASE_NAME.REGION.firebasedatabase.app
  When you enable Realtime Database, it also enables the API in the Cloud API Manager.
  Create and Initialize firebase::App
  Before you can access the Realtime Database, you'll need to create and initialize the
  Include the header file for firebase::App
  Create the firebase::App
  , passing the JNI environment and a jobject
  reference to the Java Activity as arguments:
  app = ::firebase::App::Create(::firebase::AppOptions("APPLICATION NAME"), jni_env, activity);
  Create the firebase::App
  app = ::firebase::App::Create(::firebase::AppOptions("APPLICATION NAME"));
  Access the firebase::database::Database Class
  is the entry point for the Firebase Realtime Database C++ SDK.
  ::firebase::database::Database *database = ::firebase::database::Database::GetInstance(app);
  If you have chosen to use public access for your rules, you can proceed to the sections on saving and retrieving data.
  Setting up Restricted Access
  If you do not want to use public access you can add Firebase Authentication to your app to control access to the database.
  Learn how to structure data for Realtime Database.
  Prepare to launch your app:
  - Set up budget alerts for your project in the Google Cloud console.
  - Monitor the Usage and billing dashboard in the Firebase console to get an overall picture of your project's usage across multiple Firebase services. You can also visit the Realtime Database Usage dashboard for more detailed usage information.
  - Review the Firebase launch checklist.
  - On desktop platforms (Windows, Mac, Linux), the Firebase C++ SDK uses REST to access your database. Because of this, you must declare the indexes you use with Query::OrderByChild() on desktop or your listeners will fail.
  - The desktop workflow version of Realtime Database does not support offline or persistence.