$fp = fopen('php://output', 'a');
fputs($fp, 'strings');
....
....
fclose($fp)

 /**
  * 文章訪問(wèn)日志
  * 下載的日志文件通常很大, 所以先設(shè)置csv相關(guān)的Header頭, 然后打開(kāi)
  * PHP output流, 漸進(jìn)式的往output流中寫(xiě)入數(shù)據(jù), 寫(xiě)到一定量后將系統(tǒng)緩沖沖刷到響應(yīng)中
  * 避免緩沖溢出
  */
 public function articleAccessLog($timeStart, $timeEnd)
 {
  set_time_limit(0);
  $columns = [
   '文章ID', '文章標(biāo)題', ......
  ];
  $csvFileName = '用戶日志' . $timeStart .'_'. $timeEnd . '.xlsx';
  //設(shè)置好告訴瀏覽器要下載excel文件的headers
  header('Content-Description: File Transfer');
  header('Content-Type: application/vnd.ms-excel');
  header('Content-Disposition: attachment; filename="'. $fileName .'"');
  header('Expires: 0');
  header('Cache-Control: must-revalidate');
  header('Pragma: public');
  $fp = fopen('php://output', 'a');//打開(kāi)output流
  mb_convert_variables('GBK', 'UTF-8', $columns);
  fputcsv($fp, $columns);//將數(shù)據(jù)格式化為CSV格式并寫(xiě)入到output流中
  $accessNum = '1000000'//從數(shù)據(jù)庫(kù)獲取總量，假設(shè)是一百萬(wàn)
  $perSize = 1000;//每次查詢的條數(shù)
  $pages = ceil($accessNum / $perSize);
  $lastId = 0;
  for($i = 1; $i <= $pages; $i++) {
   $accessLog = $logService->getArticleAccessLog($timeStart, $timeEnd, $lastId, $perSize);
   foreach($accessLog as $access) {
    $rowData = [
     ......//每一行的數(shù)據(jù)
    ];
    mb_convert_variables('GBK', 'UTF-8', $rowData);
    fputcsv($fp, $rowData);
    $lastId = $access->id;
   }
   unset($accessLog);//釋放變量的內(nèi)存
   //刷新輸出緩沖到瀏覽器
   ob_flush();
   flush();//必須同時(shí)使用 ob_flush() 和flush() 函數(shù)來(lái)刷新輸出緩沖。
  }
  fclose($fp);
  exit();
 }