如何使用 php 以 .dat 或 .txt 格式导出文件

I have function export_csv()to export file as .csv format. I want to change .dat or .txt format instead of .csv

当前代码:

public function export_csv() {
  
  if( ! $this->path) { throw new exception('unable to create xls: missing path'); }
       /** output conetnts to csv **/
       ob_start();
       $df = fopen($this->path.'.csv', 'w');
       foreach ($this->data as $row) {
       fputcsv($df, $row);
       }
      fclose($df);
      return $this->path;
}

我试过下面的代码.但是 .dat 文件是空白的.文件大小 0

public function export_dat() {
    
    if( ! $this->path) { throw new exception('unable to create xls: missing path'); }
    /** output contents to dat **/
        ob_start();
        $df = fopen($this->path.'.dat', 'w');
        foreach ($this->data as $row) {
            fwrite($df, $row);
        }
         fclose($df);
         
         return $this->path;
}

fwrite($df, implode(', ', $row));