我正在代码点火器中制作联系表格，但我不知道如何清除这个错误?所以我试过了

我正在代码点火器中制作联系人表格，但我不知道如何清除此错误？所以我试过了？今天只有我在使用codeigner。有人能帮我吗？我得到了错误：遇到PHP错误严重程度：通知消息：使用未定义的常量"contact_form"™ -假定为"contact_form"™'文件名：controllers/contact.php行号：33IN应用程序控制器：

<?php
    class contact extends ci_controller 
    {
        public function __construct()
        {
            parent::__construct();
        }
        public function index()
        {
            $mail_sent = false;
            if ($this->input->post("q"))
            {
                // Loading email library of Codeigniter
                $this->load->library(‘email’);
                // Loading configuration file mail_config.php
                $this->config->load(‘mail_config’,true);
                // Setting email address and name of the person sending the email
                $this->email->from($this->input->post("from"),$this->input->post("name"));
                // Setting email address of the recipient
                $this->email->to($this->config->item(‘to’,’mail_config’));
                // Setting email subject
                $this->email->subject($this->input->post("subject"));
                // Setting email message body
                $this->email->message($this->input->post("message",true));
                // If mail sending successful
                if ($this->email->send())
                {
                    // If $mail_sent = true; it will show a success message.
                    $mail_sent = true;
                }
            }
            $this->load->view(‘contact_form’,array(‘mail_sent’=>$mail_sent));
        }
    }
?>

视图中：我创建了contact_form.php

<?php 
    if ($mail_sent): 
?>
        <b>Mail Sent</b>
<?php 
    endif; 
?>
<form action="<?php echo base_url() ?>" method="POST">
    <b>Your Name :</b>
    <br />
    <input type="text" name="name"  value=""/>
    <br />
    <b>Your Email Address:</b>
    <br />
    <input type="text" name="from" value=""/>
    <br />
    <b>Subject :</b>
    <br />
    <input type="text" name="subject"  value=""/>
    <br />
    <b>Message :</b>
    <br />
    <textarea name="message" rows="10" cols="15"></textarea>
    <br />
    <input type="submit" name="q" value="Contact" />
</form>