Is there a function to make a copy of a PHP array to another?

Question

Is there a function to make a copy of a PHP array to another?

I have been burned a few times trying to copy PHP arrays. I want to copy an array defined inside an object to a global outside it.

Answer 1

In PHP arrays are assigned by copy, while objects are assigned by reference. This means that:

$a = array(); $b = $a; $b['foo'] = 42; var_dump($a); 

Will yield:

array(0) { } 

Whereas:

$a = new StdClass(); $b = $a; $b->foo = 42; var_dump($a); 

Yields:

object(stdClass)#1 (1) {   ["foo"]=>   int(42) } 

You could get confused by intricacies such as ArrayObject, which is an object that acts exactly like an array. Being an object however, it has reference semantics.

Edit: @AndrewLarsson raises a point in the comments below. PHP has a special feature called "references". They are somewhat similar to pointers in languages like C/C++, but not quite the same. If your array contains references, then while the array itself is passed by copy, the references will still resolve to the original target. That's of course usually the desired behaviour, but I thought it was worth mentioning.

Answer 2

PHP will copy the array by default. References in PHP have to be explicit.

$a = array(1,2); $b = $a; // $b will be a different array $c = &$a; // $c will be a reference to $a