You can use an object oriented interface class for a file - SplFileObject http://php.net/manual/en/splfileobject.fputcsv.php (PHP 5 >= 5.4.0)
$file = new SplFileObject('file.csv', 'a');
$file->fputcsv(array('aaa', 'bbb', 'ccc', 'ffffdd'));
$file = null;