php 下載導出csv格式

//下載合同信息
    public function actionDownload()
    {
        set_time_limit(0);
        ini_set('memory_limit', '512M');
        $criteria = new CDbCriteria();

        $rent_ids = trim(Yii::app()->request->getParam("rent_ids"));    //下載的合同列表
        //字符串轉換為數組
        if (!empty($rent_ids))
        {
            $criteria->addCondition("f_id in ({$rent_ids})");
        }

        $count = T_rent_contract::model()->count();

        //導出csv格式
        header("Content-Type:text/csv");
        header("Content-Disposition:attachment;filename=" . "_shift_agreement_detail-" . date("Y-m-d") . ".csv");
        ob_end_clean();
        $delimiter = ',';
        $table_headers = array(
            '收款人帳號',
            '收款人名稱',
            '用途',
            '金額',
        );
        $header = '';
        foreach($table_headers as $table_header)
        {
            $header .= $table_header . $delimiter;
        }
        $header = substr($header, 0, -1);
        $header .= "\n";

//        輸出表頭
        echo iconv('utf-8', 'GBK//IGNORE', $header);

        //每次取數據的步進
        $step = 1000;
        $round = ceil($count/$step);
        for($i = 1 ; $i <= $round ; $i++)
        {
            $criteria->limit = $step;    //取1條數據，如果小於0，則不作處理
            $criteria->offset = ($i - 1) * $step;   //兩條合並起來，則表示 limit 10 offset 1,或者代表了。limit 1,10
            $rent_contract_list = T_rent_contract::model()->findAll($criteria);

            if (count($rent_contract_list))
            {
                foreach($rent_contract_list as $rent_contract)
                {
                    //用途
                    $purpose = "$rent_contract->f_province_code".'-'."$rent_contract->f_store_code".'-'."$rent_contract->f_cost_center_code";
                    $f_month_pay_money = $rent_contract['f_month_pay_money'];    //固定金額
                    $f_rent = $rent_contract['f_rent'] ;          //房租

                    //合並房租和物業費
                    $table_contents = array(
                        "\t".$rent_contract->f_rent_number,  //房租賬號   \t 把數字轉字符串
                        $rent_contract->f_rent_name,    //賬號名稱(房租收款人)
                        $rent_contract->f_rent_bank,    //開戶行（房租收款人）
                        $f_month_pay_money,//固定金額,
                    );
                }

                $content = '';
                foreach($table_contents as $table_content)
                {
                    $content .= $table_content . $delimiter;
                }
                $content = substr($content, 0, -1);
                $content .= "\n";
                echo iconv('UTF-8', 'GBK//IGNORE', $content);
            }
        }
    }