我的PHP代码有错误，但找不到

Question

我创建了一个忘记密码的脚本。但是，当我要求发送一封电子邮件给我以更改该消息的密码时，会向我发送消息：

单击“忘记密码”并输入出现的电子邮件：

  

严重错误：调用未定义的函数random_bytes（）   C：\ wamp64 \ www \ app_logic.php在第51行

我是编程的初学者。

代码：

   <?php 

     session_start();
     $errors = [];
     $user_id = "";
      // connect to database
     $db = mysqli_connect('localhost', 'root', '', 'registration');

      // LOG USER IN
     if (isset($_POST['login_user'])) {
      // Get username and password from login form
      $user_id = mysqli_real_escape_string($db, $_POST['user_id']);
      $password = mysqli_real_escape_string($db, $_POST['password']);
       // validate form
       if (empty($user_id)) array_push($errors, "Username or Email is        required");
      if (empty($password)) array_push($errors, "Password is required");

      // if no error in form, log user in
      if (count($errors) == 0) {
      $password = md5($password);
      $sql = "SELECT * FROM users WHERE username='$user_id' OR  email='$user_id' AND password='$password'";
      $results = mysqli_query($db, $sql);

       if (mysqli_num_rows($results) == 1) {
       $_SESSION['username'] = $user_id;
       $_SESSION['success'] = "You are now logged in";
       header('location: index.php');
       }else {
       array_push($errors, "Wrong credentials");
          }
        }
       }

      /*
      Accept email of user whose password is to be reset
      Send email to user to reset their password
      */
       if (isset($_POST['reset-password'])) {
       $email = mysqli_real_escape_string($db, $_POST['email']);
      // ensure that the user exists on our system
      $query = "SELECT email FROM users WHERE email='$email'";
      $results = mysqli_query($db, $query);

      if (empty($email)) {
      array_push($errors, "Your email is required");
      }else if(mysqli_num_rows($results) <= 0) {
      array_push($errors, "Sorry, no user exists on our system with that  email");
       }
      $token="";
      // generate a unique random token of length 100
      $token = bin2hex(random_bytes(50));

      if (count($errors) == 0) {
      // store token in the password-reset database table against the user's email
      $sql = "INSERT INTO password_reset(email, token) VALUES ('$email',   '$token')";
      $results = mysqli_query($db, $sql);

      // Send email to user with the token in a link they can click on
      $to = $email;
      $subject = "Reset your password on examplesite.com";
      $msg = "Hi there, click on this <a href=\"new_password.php?token=" .  $token . "\">link</a> to reset your password on our site";
      $msg = wordwrap($msg,70);
      $headers = "From: info@examplesite.com";
      mail($to, $subject, $msg, $headers);
      header('location: pending.php?email=' . $email);
        }
      }

      // ENTER A NEW PASSWORD
     if (isset($_POST['new_password'])) {
      $new_pass = mysqli_real_escape_string($db, $_POST['new_pass']);
      $new_pass_c = mysqli_real_escape_string($db, $_POST['new_pass_c']);

     // Grab to token that came from the email link
     $token = $_SESSION['token'];
     if (empty($new_pass) || empty($new_pass_c)) array_push($errors, "Password is required");
     if ($new_pass !== $new_pass_c) array_push($errors, "Password do not match");
      if (count($errors) == 0) {
      // select email address of user from the password_reset table 
      $sql = "SELECT email FROM password_reset WHERE token='$token' LIMIT 1";
      $results = mysqli_query($db, $sql);
     $email = mysqli_fetch_assoc($results)['email'];

      if ($email) {
      $new_pass = md5($new_pass);
      $sql = "UPDATE users SET password='$new_pass' WHERE email='$email'";
      $results = mysqli_query($db, $sql);
       header('location: index.php');
           }
         }
       }
       ?>