PHP產生隨機不重復激活碼

    /**
     * 生成激活碼
     */
    public function create_cdk()
    {
        if (IS_POST) {
            $cdk_num = intval(I('post.cdk_num'));  //生成數量
            if ($cdk_num) {
                for ($i = 0; $i < $cdk_num; $i++) {
                    //查詢是否重復
                    //$cdkey=create_randomstr_s();
                    $check = true;
                    while ($check==true) {
                        $cdkey = create_randomstr_s();
                        $result = M('course_cdkey')->where(array('cdkey' => $cdkey))->find();
                        if (empty($result)) {
                            $data['cdkey'] = $cdkey;
                            $check = false;
                        }
                    }
                    $data['validity']=I('post.validity');
      
                    $data['addTime']=time();
                    $result=M('course_cdkey')->add($data);
                }
                if($result){
                    $this->success('操作成功');
                }
            }
        } else {
            $this->display('create_cdk');
        }

    }

/**
 * 生成隨機字符串（數字字母小寫）
 * @param string $lenth 長度
 * @return string 字符串
 */
function create_randomstr_s($lenth = 6) {

    return random($lenth, '123456789abcdefghijklmnpqrstuvwxyz');

}