sqlite3_db_filename —
Return The Filename For A Database Connection
const char *
sqlite3_db_filename(sqlite3 *db,
  const char *zDbName);
The sqlite3_db_filename(D,N) interface returns a pointer to a filename
  associated with database N of connection D. The main database file has the
  name "main". If there is no attached database N on the database
  connection D, or if database N is a temporary or in-memory database, then a
  NULL pointer is returned.
The filename returned by this function is the output of the
    xFullPathname method of the VFS. In other words, the filename will be an
    absolute pathname, even if the filename used to open the database originally
    was a URI or relative pathname.