Some helper functions for CodeIgniter Cart Library. With this functions you can get all ids of your cart and also check if the id is in the cart.

cart_helper.php

<?php

/* cart helper */

function is_item_in_cart($id) {
    return in_array($id, get_cart_item_ids());
}

function get_cart_item_ids() {
    $CI   =& get_instance();
    $cart = $CI->cart->contents();
    
    $cart_ids = array_map(function($element) {
        return $element['id'];
    }, $cart);

    return $cart_ids;
}

function get_row_id_by_item($item_id) {
    $items = get_cart_item_ids();
    return array_search($item_id, $items);
}

Tested with CI 2.1.3

[cart_contents] => Array
        (
            [0185acd2e0e6a4e58e0b222dacf38497] => Array
                (
                    [rowid] => 0185acd2e0e6a4e58e0b222dacf38497
                    [id] => 1234
                    [qty] => 1
                    [price] => 10.00
                    [name] => My New Product
                    [options] => Array
                        (
                            [thumbnail] => http:/example.com/thumb1234.png
                            [foo] => bar
                        )

                    [subtotal] => 10.00
                )

            [total_items] => 1
            [cart_total] => 1
        )

is_item_in_cart(1234) returns true
is_item_in_cart(4321) returns false

---

get_cart_item_ids() returns

Array (
0185acd2e0e6a4e58e0b222dacf38497 => 1234
)

---

get_row_id_by_item(1234) returns 0185acd2e0e6a4e58e0b222dacf38497
get_row_id_by_item(4321) returns false