sqlite3_file *sqlite3_database_file_object(const char*);
If X is the name of a rollback or WAL-mode journal file that is passed into the xOpen method of sqlite3_vfs, then sqlite3_database_file_object(X) returns a pointer to the sqlite3_file object that represents the main database file.
This routine is intended for use in custom VFS implementations only. It is not a general-purpose interface. The argument sqlite3_file_object(X) must be a filename pointer that has been passed into sqlite3_vfs.xOpen method where the flags parameter to xOpen contains one of the bits SQLITE_OPEN_MAIN_JOURNAL or SQLITE_OPEN_WAL. Any other use of this routine results in undefined and probably undesirable behavior.
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