Sqlite3 extension

/*
** An array of pointers to extension initializer functions for
** built-in extensions.
*/
static int (*const sqlite3BuiltinExtensions[])(sqlite3*) = {
#ifdef SQLITE_ENABLE_FTS3
  sqlite3Fts3Init,
#endif
#ifdef SQLITE_ENABLE_FTS5
  sqlite3Fts5Init,
#endif
//...

/*
** This routine does the work of opening a database on behalf of
** sqlite3_open() and sqlite3_open16(). The database filename "zFilename"
** is UTF-8 encoded.
*/
static int openDatabase(
  const char *zFilename, /* Database filename UTF-8 encoded */
  sqlite3 **ppDb,        /* OUT: Returned database handle */
  unsigned int flags,    /* Operational flags */
  const char *zVfs       /* Name of the VFS to use */
){
  // ...
  /* Load compiled-in extensions */
  for(i=0; rc==SQLITE_OK && i<ArraySize(sqlite3BuiltinExtensions); i++){
    rc = sqlite3BuiltinExtensions[i](db);
  }

  /* Load automatic extensions - extensions that have been registered
  ** using the sqlite3_automatic_extension() API.
  */
  if( rc==SQLITE_OK ){
    sqlite3AutoLoadExtensions(db);
    rc = sqlite3_errcode(db);
    if( rc!=SQLITE_OK ){
      goto opendb_out;
    }
  }
  // ...
}

• https://www.sqlite.org/loadext.html