Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent

index.php
<?php
 
include ('cart_fns.php');
 
session_start();
if(!isset($_SESSION['cart']))
{
    $_SESSION['cart'] = array();
    $_SESSION['total_items'] = 0;
    $_SESSION['total_price'] = '0.00';
}
 
 
 
 
$view = empty($_GET['view']) ? 'index' : $_GET['view'];
 
include($_SERVER['DOCUMENT_ROOT'].'/catalog/views/layouts/shop.php');

cart.php //Корзина
 
<?php
$id = $_GET['id'];
$add_item = add_to_cart($id);
header('Location: index.php?view=product&id='.$id);
?>
 
<h2 align="center">Ваша корзина товаров</h2>
 
<form action="" method="post" id="cart-form">
 
<table id="mycart" align="center" cellspacing="0" cellpading="0" border="1" width="700" height="60">
<tr>
<th>Цена</th>
<th>Кол-во</th>
<th>Всего</th>
</tr>
 
<tr colspan="4">
<td align="center"></td>
<td align="center">Руб.</td>
<td align="center"><input type="text" size="2" name="" maxlength="2" value=""/> </td>
<td align="center">Руб.</td>
 
</tr>
</table>
<br />
    <p class="total" align="center">Общая сумма заказа:<span class="product-price">Руб.</span></p><br />
    <p align="center"><input type="submit" name="update" value="Обновить" /></p>
    </form>

cart_fns.php
 
<?php
function add_to_cart($id)
{
    if(isset($_SESSION['cart'][$id]))
    {
        $_SESSION['cart'][$id]++;
        return true;
    }
    else
    {
      $_SESSION['cart'][$id] = 1;
      return true;
    }
    return false;
    }
?>