Warning: unable to change header information - headers already submitted (PHP)

Question

My problem is somewhat similar to the following post.

PHP error: unable to change header information - headers already submitted

But in my case, I decided to start the session as soon as I determine that there are no verification errors in the login form, and the login information matches the database information. Here is the following code:

Login page (before any html)

session_name('username');
session_name('ip');
session_name('start');
session_start();    

Checkbox Login.php (in html body)

         } else {
            $user = $_POST['username']; 
            $userpass = md5($_POST['password']); 
            $login_results = statement("select username, password from `$admin` where username='$user' and password='$userpass'");

            if (mysql_num_rows($login_results)!= 1) { 
                $errmsg = "<span id='error'>Login failed: Username or password not on file</span>";
            }else {

                $_SESSION['username'] = "$user"; 
                $_SESSION['ip'] = $_SERVER['REMOTE_ADDR'];
                header("Location: index.php"); 
            }
        }
    }

}

If you look at the else block above the code, I check the login and, if it's good, I want to assign session variables and go to my index page. Which has this code at the very beginning:

 //Session Timeout Script -- used to determine the amount of time the user has been idle.  If it the user has been idle for longer then the session time, log the user out.
 //Secondary to the Timeout Script, the username and ip address is checked for validility and if either fails redirect the user to the login page. 
 session_cache_expire( 20 );
 session_start(); 

 $inactive = 1200;     

 if(isset($_SESSION['start']) ) {
      $session_life = time() - $_SESSION['start'];
  if($session_life > $inactive){
        header("Location: logout.php");
   }
}

  $_SESSION['start'] = time();

    $newip = $_SERVER['REMOTE_ADDR']; 
   if (!isset($_SESSION['username']) ||  empty($_SESSION['username']) || $newip!=    $_SESSION['ip']) { 
 header('Location: login.php'); 
} 

, , , header() , , , - login.php. , , header(), . , , , . ? , login.php?

Answer 1

, header , http, . session_start().

, , $_POST html-.

Btw, session_name ?

Answer 2

.
, .php .
- :

   <?php
//Codes...

, PHP . , PHP- HTML.
, session_start() PHP.
, .

Answer 3

You can also use output buffering. See the PHP Manual in OB Tasks .