$ _FILES [＆＃39; file_upload＆＃39;] [＆＃39; tmp_name＆＃39;]未定义

Question

我正在写一个上传文件页面。这是html代码：

<form action="verify.php" id="upload" method="post" enctype="multipart/form-data">
<input id="file_upload" type="file" name="file_upload" />
<button id="submit" name="submit" type="submit">Upload</button>
</form>

这是我的PHP代码：

if ($_FILES['file_upload']['error']==UPLOAD_ERR_NO_FILE){
    return;
  }  
  try{
    $email_add='MY@gmail.com';
    $subject="Driver Verification";
    $mail = $this->emailConfig();      
    $mail->addAddress($email_add, "LALALA");  // Add a recipient
    $mail->Subject = $subject;
    echo $_FILES['file_upload']['name'];
    echo $_FILES['file_upload']['tmp_name'];
    $mail->Body    = "This driver requires a verification."
    $mail->AddAttachment($_FILES['file_upload']['tmp_name'],$_FILES['file_upload']['name']);
    if(!$mail->send()) {
      echo 'Message could not be sent.';
      echo 'Mailer Error: ' . $mail->ErrorInfo;
      exit;
    }
    return;     
  }
  catch(PDOException $e){
    return;
  }
}

因此，当我运行代码时，它只能回显[＆＃39; name＆＃39;]但不能回显[＆＃39; tmp_name＆＃39;]，因此没有电子邮件附件。

有什么想法？感谢。