尝试使用php发送电子邮件时出错

我有这一页

使用我得到的html代码

我在php代码的第65行得到一个错误。。错误是

注意：在中使用未定义的常量-假定为“” C:\wamp\www\mTest\send\u form\u email.php，第65行

顺便说一句，我不需要数据库来做这件事，是吗？ php代码：

 <?php
    if(isset($_POST['email'])) {
     
    // EDIT THE 2 LINES BELOW AS REQUIRED
    $email_to = "you@yourdomain.com";
    $email_subject = "Your email subject line";
     
     
    function died($error) {
        // your error code can go here
        echo "We are very sorry, but there were error(s) found with the form you submitted. ";
        echo "These errors appear below.<br /><br />";
        echo $error."<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }
     
    // validation expected data exists
    if(!isset($_POST['first_name']) ||
        !isset($_POST['last_name']) ||
        !isset($_POST['email']) ||
        !isset($_POST['telephone']) ||
        !isset($_POST['comments'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');       
    }
     
    $first_name = $_POST['first_name']; // required
    $last_name = $_POST['last_name']; // required
    $email_from = $_POST['email']; // required
    $telephone = $_POST['telephone']; // not required
    $comments = $_POST['comments']; // required
     
    $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
  if(!preg_match($email_exp,$email_from)) {
    $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
  }
    $string_exp = "/^[A-Za-z .'-]+$/";
  if(!preg_match($string_exp,$first_name)) {
    $error_message .= 'The First Name you entered does not appear to be valid.<br />';
  }
  if(!preg_match($string_exp,$last_name)) {
    $error_message .= 'The Last Name you entered does not appear to be valid.<br />';
  }
  if(strlen($comments) < 2) {
    $error_message .= 'The Comments you entered do not appear to be valid.<br />';
  }
  if(strlen($error_message) > 0) {
    died($error_message);
  }
    $email_message = "Form details below.\n\n";
     
    function clean_string($string) {
      $bad = array("content-type","bcc:","to:","cc:","href");
      return str_replace($bad,"",$string);
    }
     
    $email_message .= "First Name: ".clean_string($first_name)."\n";
    $email_message .= "Last Name: ".clean_string($last_name)."\n";
    $email_message .= "Email: ".clean_string($email_from)."\n";
    $email_message .= "Telephone: ".clean_string($telephone)."\n";
    $email_message .= "Comments: ".clean_string($comments)."\n";
     
     
// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);  
?> //line 65
 
<!-- include your own success html here -->
 
Thank you for contacting us. We will be in touch with you very soon.
 
<?php
}
?>

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这就是为什么你要学习一门语言，而不仅仅是复制和粘贴它。。我在学校学习HTML，我试着自己学习PHP，但单独学习并不容易……died是否存在？@liam看到函数died line 10~，所以它存在。died是在代码顶部定义的，第65行是什么