php://outputが書き込みの途中で出力される - Qiita

<?php $array = getArray(); // BDとから取得 $file = new SplFileObject('php://output', 'w'); foreach($array as $row) { $file->fputcsv($row); } header('Content-Type: application/octet-stream'); header('Content-Disposition: attachment; filename=sample.csv'); header('Content-Transfer-Encoding: binary'); $file->fflush(); $arrayの中身が大きくなると Warning: Cannot modify header information - headers already sent by がでた