What procedures or processes are performed by the system before calling the main function during program startup?

Before calling the main function when launching an iOS application, the system performs several important procedures:

1. Initialization of the application runtime environment.
2. Loading and preparing application resources.
3. Calling the application(_:willFinishLaunchingWithOptions:) method in the application delegate for initial setup.
4. Calling the application(_:didFinishLaunchingWithOptions:) method, where the main initialization, UI setup, and services usually occur.

After this, the system displays the main window and begins processing user events. These methods help prepare the application for operation before the user sees the interface.