void *sqlite3_user_data(sqlite3_context*);
The sqlite3_user_data() interface returns a copy of the pointer that was the pUserData parameter (the 5th parameter) of the sqlite3_create_function() and sqlite3_create_function16() routines that originally registered the application defined function.
This routine must be called from the same thread in which the application-defined function is running.
See also lists of Objects, Constants, and Functions.
SQLite is in the Public Domain.
https://sqlite.org/c3ref/user_data.html