echo I('get.id',100); echo I('get.name','NoBody');

    //http://localhost/thinkphp323/index.php/home/User/I?id=&name=
    public function I(){
        echo I('get.id',100); // 如果不存在$_GET['id'] 则返回100
        echo '<br>';
        echo I('get.name','NoBody'); // 如果不存在$_GET['name'] 则返回NoBody
    }

http://localhost/thinkphp323/index.php/home/User/I?id=111&name=Yum

111
Yum