Cut out base string of filename from filepath. If base is null, then return length that require for store base name.
Cut out directroy string from filepath. If dir is null, then return length that require for store directory.
Cut out extension of filename or filepath. If ext is null, then return length that require for store extension.
Cut out filename string from filepath. If name is null, then return length that require for store directory.
Generate file full path name.