如何过滤进入CSV文件的数据?

我试图使用数据库中的值生成CSV文件并强制下载它。除了文件从服务器拾取(不相关的)错误消息并将其包含在CSV文件中之外，它工作得很好。我如何防止这种情况发生?

下面是我的函数:

public function export($coupons_ids) {
        $coupons_ids = explode(',', (urldecode($coupons_ids)));
        $result = $this->cart_coupons->get_where_in('id',array_filter($coupons_ids, 'strlen'));
        header('Content-Type: text/csv; charset=utf-8');
        header('Content-Disposition: attachment; filename=coupons.csv');
        $output = fopen('php://output', 'w');
        fputcsv($output, array('id', 'name', 'start_date', 'end_date', 'promo', 'usage_limit'));
        foreach ($result as $row)
        {
            $id = $row->id;
            $name = $row->name;
            $start_date = $row->start_date;
            $end_date = $row->end_date;
            $usage_limit = $row->usage_limit;
            $active = '';
            switch($row->active)
            {
            case 0:
                $active = 'YES';
                break;
            case 1:
                $active = 'NO';
                break;
            }
            $promo = '$0';
            switch($row->promo_type)
            {
            case 0:
                $promo = '$' . $row->promo_value;
                break;
            case 1:
                $promo = $row->promo_value . '%';
                break;
            }
            $data = array('id' => $id, 'name' => $name, 'start_date' => $start_date, 'end_date' => $end_date, 'promo' => $promo, 'usage_limit' => $usage_limit);
            fputcsv($output, $data);
        }
        fclose($output);
    }

输出为:

<br />
<b>Strict Standards</b>:  Only variables should be passed by reference in <b>D:'xampp'htdocs'----'-----.php</b> on line <b>245</b><br />
id,name,start_date,end_date,promo,usage_limit
3,Test3,"2013-03-12 00:00:00","2013-03-20 00:00:00",$500,10
4,Test4,"2013-03-17 00:00:00","2013-04-25 00:00:00",25%,50
5,Test5,"2013-03-20 00:00:00","2013-03-25 00:00:00",$40,1000
6,Test6,"2013-03-12 00:00:00","2013-03-20 00:00:00",$50,100
7,Test7,"2013-03-15 00:00:00","2013-03-28 00:00:00",10%,150
81,CC00016,"2013-04-20 00:00:00","2013-04-27 00:00:00",$100,10
80,CC00015,"2013-04-16 00:00:00","2013-04-23 00:00:00",$100,1
79,CC00014,"2013-04-16 00:00:00","2013-04-23 00:00:00",$100,1
78,CC00013,"2013-04-16 00:00:00","2013-04-23 00:00:00",$100,1
76,CC00011,"2013-04-16 00:00:00","2013-04-23 00:00:00",$100,1
77,CC00012,"2013-04-16 00:00:00","2013-04-23 00:00:00",$100,1

我知道这个错误是什么，它与代码的功能完全无关。