Codeigniter购物车：添加负价

I'm trying to add a negative price in Codeingiter Cart but cannot.

$coupon = array(
    'id' => $result->id,
    'name' => $result->name,
    'qty' => '1',
    'price' => $result->discount,
    'options' => array(
        'info' => 'coupon',
        'qty_description' => '')
    );
$this->cart->insert($coupon);

Where $result->discount is taken from a DB and is a Decimal number -20.

When I use this code I get the item in the cart but it turns it into (+)20 and not -20. Any reason and help on this?

Check the cart library in system/libraries/Cart.php line #194:

            // Prep the price.  Remove anything that isn't a number or decimal point.
        $items['price'] = trim(preg_replace('/([^0-9\.])/i', '', $items['price']));
        // Trim any leading zeros
        $items['price'] = trim(preg_replace('/(^[0]+)/i', '', $items['price']));

        // Is the price a valid number?
        if ( ! is_numeric($items['price']))
        {
            log_message('error', 'An invalid price was submitted for product ID: '.$items['id']);
            return FALSE;
        }

so basically codeigniter is only accepting positive values, you can change those lines but be-careful when upgrading or you can extend the library class and add another custom key.

You should only add a - sign after . in this function

preg_replace('/([^0-9\.])/i', '', $items['price'])

in cart library exist here system/libraries/Cart.php line #194: after adding it will be look like

preg_replace('/([^0-9\.-])/i', '', $items['price'])