CODEWITHSUNDEEP
phparrays
jd182
jd182

Reputation: 3260

PHP referencing array instead of copying

I have an array, I need to copy the first item in the array and alter it.

This is what i'm doing:

echo $QuantityDiscounts[0]['price'] . '<br>';
echo $QuantityDiscounts[0]['from_quantity'] . '<br>';

$firstItem                  = $QuantityDiscounts[0];
$firstItem['from_quantity'] = 999;
$firstItem['price']         = 999;

echo $QuantityDiscounts[0]['price'] . '<br>';
echo $QuantityDiscounts[0]['from_quantity'] . '<br>';

This is the output this gives me:

4.870000
10
4.870000
999

When I change the value of the copied array it's changing the original array. What makes this even stranger is that it only happens for the 'from_quantity' item. As you can see the 'price' element remains unaltered.

I can't figure out why this is happening, as you can see i'm not using references. Is there an explanation for this behaviour that i'm missing?

Some more info:

If I first copy the 'from_quantity' in the original array so that it uses a different key this behaviour goes away.

$QuantityDiscounts[0]['test'] = $QuantityDiscounts[0]['from_quantity'];

echo $QuantityDiscounts[0]['price'] . '<br>';
echo $QuantityDiscounts[0]['from_quantity'] . '<br>';
echo $QuantityDiscounts[0]['test'] . '<br>';

$firstItem = $QuantityDiscounts[0];
$firstItem['from_quantity'] = 999;
$firstItem['test']          = 999;
$firstItem['price']         = 999;

echo $QuantityDiscounts[0]['price'] . '<br>';
echo $QuantityDiscounts[0]['from_quantity'] . '<br>';
echo $QuantityDiscounts[0]['test'] . '<br>';

Outputs:

4.870000
10
10
4.870000
999
10

** UPDATE ** - Thanks for your help so far

Here is the function that generates the array. I can see that a reference is being used there which must be causing the problems. Does this mean I can't copy and modify the 'from_quantity' without changing the original?

protected function formatQuantityDiscounts($specific_prices, $price, $tax_rate, $ecotax_amount)
{
    foreach ($specific_prices as $key => &$row)
    {
        $row['quantity'] = &$row['from_quantity'];
        if ($row['price'] >= 0) // The price may be directly set
        {
            $cur_price = (Product::$_taxCalculationMethod == PS_TAX_EXC ? $row['price'] : $row['price'] * (1 + $tax_rate / 100)) + (float)$ecotax_amount;
            if ($row['reduction_type'] == 'amount')
                $cur_price -= (Product::$_taxCalculationMethod == PS_TAX_INC ? $row['reduction'] : $row['reduction'] / (1 + $tax_rate / 100));
            else
                $cur_price *= 1 - $row['reduction'];
            $row['real_value'] = $price - $cur_price;
        }
        else
        {
            if ($row['reduction_type'] == 'amount')
                $row['real_value'] = Product::$_taxCalculationMethod == PS_TAX_INC ? $row['reduction'] : $row['reduction'] / (1 + $tax_rate / 100);
            else
                $row['real_value'] = $row['reduction'] * 100;
        }
        $row['nextQuantity'] = (isset($specific_prices[$key + 1]) ? (int)$specific_prices[$key + 1]['from_quantity'] : -1);
    }
    return $specific_prices;
}

Upvotes: 1

Views: 110

Answers (2)

Denis Lins
Denis Lins

Reputation: 814

The most plausible cause of your problem is that your variable points to a object, and not to an array. Acessing objects as arrays is very simple through the ArrayAccess interface, and because it points to a object (and objects are always passed as references), the value changes. Clone the variable before making any changes.

The other probably reason is that you are explicit using references. In this case, you have to find where the problem lies and fix it by yourself, as we don't have access to your application.

Upvotes: 0

Kaii
Kaii

Reputation: 20540

If $QuantityDiscounts[0]['from_quantity'] already IS a reference, you don't need to reference it again - it will stay a reference and the reference will be copied on assignment, instead of the actual value.

This code demonstrates what i mean:

$foo = 10;

$QuantityDiscounts[0]['price'] = 4.870000;
$QuantityDiscounts[0]['from_quantity'] =& $foo;
$firstItem                  = $QuantityDiscounts[0];
$firstItem['from_quantity'] = 999;
$firstItem['price']         = 999;

echo $QuantityDiscounts[0]['price'] . '<br>';
echo $QuantityDiscounts[0]['from_quantity'] . '<br>';

Outputs:

4.87
999    (instead of the initial value 10 !)

To get a real COPY of your array (and all its elements) you need to manually dereference the child elements. Unfortunately, PHP has no built-in method for that, yet.

See this QA on StackOverflow on how to dereference array elements while copying.

Upvotes: 1

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