我应该在哪里放filter_var（$ email_address，FILTER_VALIDATE_EMAIL）？

Question

我不知道该将filter_var ($ email_address, FILTER_VALIDATE_EMAIL)放在此代码中的哪个位置？

$hiddenfield = md5("d-m-Y-l");
$passwordhash = '%_&!KJ:FLA)809-25j;LKJF:LKJAP*^@)';
$ww = hash('SHA512', md5(sha1('Test' . $passwordhash)));
if (isset($_POST['register'])) {
  if (isset($_POST['hiddenfield']) == $hiddenfield) {
    if (isset($_POST['username']) && isset($_POST['email']) && isset($_POST['password']) && isset($_POST['password2'])) {
      if (strlen($_POST['username']) >= 3) {
        $email = $db->escape_string($_POST['email']);
        if ($selectemail = $db->query("SELECT * FROM gebruikers WHERE email='$email'")) {
          if ($selectemail->num_rows == 0) {
        $ww1 = $db->escape_string($_POST['password']);
        $ww2 = $db->escape_string($_POST['password2']);
        if ($ww1 == $ww2) {
          if (strlen($ww1) >= 6) {
            $ip = $db->escape_string($_SERVER['REMOTE_ADDR']);
            if ($ipc = $db->query("SELECT * FROM gebruikers WHERE ip='$ip'")) {
              if ($ipc->num_rows < 3) {
                $username = $db->escape_string(htmlentities($_POST['username']));
                $passwordQ = $_POST['password'];
                $password = $db->escape_string(hash('SHA512' , md5(sha1($passwordQ . $passwordhash))));
                $email = $db->escape_string($_POST['email']);
                $forgot_idf = substr(str_shuffle(str_repeat("0123456789abcdefghijklmnopqrstuvwxyz!@#$%^&*()-ABCDEFGHIJKLMNOPQRSTUVWXYZ?><`~", 5)), 0, 25);
                $active_code = $db->escape_string(md5($forgot_idf));
                $register_on = date("F Y");
                if ($insertregister = $db->query("INSERT INTO gebruikers (username, password, rankid, register_on, active, active_code, email, ip) VALUES ('$username','$password','1','$register_on', '0', '$active_code', '$email', '$ip')")) {
                 $error2 = 'Account is created!';
                } else {
                  echo 'Query is incorrect! ' . $db->error;
                }
              } else {
                $error = 'You have already registered more than 3 accounts!';
              }
            }
          } else {

             $error = 'Your password must be at least 6 characters!';
          }
        } else {

           $error = 'The passwords do not match!';
        }
        } else {

            $error = 'This email address has been used once before!';
          }
        } else {
          echo 'Query is incorrect! ' . $db->error;
        }
      } else {

        $error = 'Your username must contain at least 3 letters!';

      }
    }
  }
}

我已经尝试了一切。 有人可以添加filter_var ($ email_address, FILTER_VALIDATE_EMAIL)吗？