php致命错误:调用成员函数

我的代码是:

 $soap_location,
                                     'uri'      => $soap_uri,
                                     'trace' => 1,
                                     'exceptions' => 1));

try {
    if($session_id = $client->login($username,$password)) {
        echo 'Logged successfull. Session ID:'.$session_id.'
';
    }

    //* Set the function parameters.
    $client_id = 2;

    function ftpadduser()
    {

        $params = array(
                        'server_id' => 1,
                        'parent_domain_id' => 1,
                        'username' => 'threep',
                        'password' => 'wood',
                        'quota_size' => 10,
                        'active' => 'y',
                        'uid' => '5000',
                        'gid' => '5000',
                        'dir' => 'maybe',
                        'quota_files' => -1,
                        'ul_ratio' => -1,
                        'dl_ratio' => -1,
                        'ul_bandwidth' => -1,
                        'dl_bandwidth' => -1
                        );

        $affected_rows = $client->sites_ftp_user_add($session_id,$client_id, $params);

        echo "FTP User ID: ".$affected_rows."
";

    }

    ftpadduser();

    if($client->logout($session_id)) {
        echo 'Logged out.
';
    }


} catch (SoapFault $e) {
    echo $client->__getLastResponse();
    die('SOAP Error: '.$e->getMessage());
  }

?>

虽然在这种情况下,如果我不以某种方式使用函数,我能够运行一切,但它给了我

Logged successfull. Session ID:9a46b41e293ff9d5d5604648013caf76

Fatal error: Call to a member function sites_ftp_user_add() on a non-object in C:\xampp\htdocs\img\client_get.php on line 39

作为输出,我想知道是否有人可以帮助我如何运行此功能,并避免致命错误.

谢谢