php中未定义的索引错误是什么？ [关闭]

error: "Notice: Undefined index: page in C:\wamp\www\digi\admin\config\setup.php on line 8"

my code is:

    <?php
   #setup document
                      //host-username-password-database_name
   $db = mysqli_connect('localhost','root','','dynamic');

   if($_GET['page'] == "")
               {$pg = 'home';}
   else
               {$pg = $_GET['page'];}

   include('/functions/sandbox.php');

   include('/functions/template.php');

   $page_title =  get_page_title($db,$pg);
?>

$_GET['page'] is not defined. To correctly check if it exists you should use isset():

 if(isset($_GET['page'])) {$pg = 'home';} else {$pg = $_GET['page'];}