Notice: Undefined index: username 什么原因？？？？

Question

$mysqli->set_charset('utf8');

$username=$_POST['username'];

$username=$mysqli->escape_string($username);//转义字符串，例如特殊字符

$password=md5($_POST['password']);

$age=$_POST['age'];

$act=$_GET['act'];

$id=$_GET['id'];

什么原因？？？？

错误提示：

Notice: Undefined index: username

 Notice: Undefined index: password

Notice: Undefined index: age

Answer 1

UEUIBBXOKFCVBRXDDPVRLFXUGQEHVZCMMMSUUOOEFOOLPFFBBLIHKNNDKNYIRGOTVYNTCFNZDADZDUAVSIQMJOEYMFFBVFPPIHLOXQBEWMFVNTNGHUPQSKAGDDNNXXXXNGTDEUKMWIZIEIYJJWGNIHXAUENNOBKOFFOOHEMCTTYRXXQKJMCLOEHWMJMORILWGWDVMWGGADTEJAJAHXGJZPSBMHXHBLRWGSTJZGZYUQZPMCZBRBUQFPYIFVEHQLUJZPGCZBKUGWGQFQADTDTQZQZPRPLHDTSHDAPSVEADGTQLJYBWMBTVEAPUWMJZIFHNCSQNJSDSBYRORPFOEGWGCGPYCZCXCFUFNWSBRVRHXTDQTIGCKAQSDZZVXHFUCZCLJVFNQUDLVQNWJFAQGWZCLOETVZUXNKNCZDYVYIEHQMIYIHJFWNYIESPFZOLOFWNXMPFLVEOSILVQZDEGCSVRHPRHKFVSZSPQTWGTXGIYOKGPSOLYOLBYBEBJBRUKUQGJZPRAIEAPNWHQFISIGIRHLVLOXAJBEYHEUJFVZCFOWTJAQFOEBEPIOLLULLEMWIOPHHLYOBIEHGGGGGSCFMFAGKQGZXWRHFLFIYKOEURHYUADKHTGZGJECFFIWPFVCSLHAHUWJQHRHOYEICFCSILTZMCPJTUTWJTXTWJTMMCFFZVOEHQAUUHXHSUREZCFWMGPRQDGGGVVNAMGGXHEVVBRUPNGBKLLLFLFFNAZSSMTGVBKWZQUTXCMYTJUPVLSMVNJTTBHFIIREVSPCPMGJWWPPYZTPFFGGATBDLRUWZMKDKKHWWDGKEHXXDJJKGYOOIMFMSZZLRXRFECCLVVHJMLLESYXHMVSGWMWCPFCIHKJPJKNQFMP

Answer 2

Undefined未定义你要的值

Answer 3

你先查看一下你的POST是否有数据吧!!var_dump($_POST)..然后你就知道了