php - "Undefined" Error on another web server while everything is fine on local server -

i have run script many times on local server , there no problem. when uploaded them on web server faced undefined errors. confused.

what problem??

database tables defined.

php version on local: 5.3.5, on web server: 5.3.26

i these errors:

            php error encountered              severity: notice             message:  undefined index: username             filename: models/user.php             line number: 7              php error encountered              severity: notice             message:  undefined index: password             filename: models/user.php             line number: 8              php error encountered              severity: warning             message:  cannot modify header information - headers sent (output started @ /home/caspian/domains/caspiansang.ir/public_html/system/core/exceptions.php:185)             filename: views/login.php             <p>line number: 1 

controller/verifylogin.php:

            <?php if ( ! defined('basepath')) exit('no direct script access allowed');              class verifylogin extends ci_controller {               function __construct()              {                parent::__construct();                $this->load->model('user','',true);              }               function index()              {                      $result = $this->user->validate();                     if(! $result){                      $data['msg'] = 'اطلاعات وارد شده اشتباه است!';                     $this->load->view('login',$data);                     }else{                         redirect('admin');                     }                         }               } 

models/user.php

            <?php             class user extends ci_model             {               public function validate(){                      $username = $_post['username'];                     $password = $_post['password'];                       // prep query                     $this->db->where('username', $username);                     $this->db->where('password', md5($password));                      // run query                     $query = $this->db->get('admin');                     // let's check if there results                     if($query->num_rows() == 1)                     {                         // if there user, create session data                         $row = $query->row();                         $data = array(                                 'userid' => $row->userid,                                 'fname' => $row->fname,                                 'lname' => $row->lname,                                 'username' => $row->username,                                 'validated' => true                                 );                         $this->session->set_userdata($data);                         return true;                     }                      return false;                 }               } 

views/login.php:

       <?php echo form_open('verifylogin'); ?>            <br>                     <div style="font-color:black; padding-bottom:10px;"> <?php if(!   empty($msg)) echo $msg;?></div>                   < label for="username">نام کاربری</label>          <input type="text" size="20" id="username" name="username"/>          <br/>          <label for="password">رمز عبور</label>          <input type="password" size="20" id="passowrd" name="password"/>          <br/> 

you have display_errors turned off on 1 server , on on other. issues still occur on both servers, don't told them on one.

the issue accessing variables or parts of arrays not defined before try use them.