Ampersand before a variable in foreach php

Question

I have seen an ampersand symbol before a variable in foreach. I know the ampersand is used for fetching the variable address which is defined earlier.

I have seen a code like this:

<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
}

// $arr is now array(2, 4, 6, 8)
unset($value); // break the reference with the last element

?>

I just need to know the use of & before $value. I haven't seen any variable declared before to fetch the variable address.

Please help me why its declared like this. Any help would be appreciated.

does it has any problem if we didnt declaire it without an ambersand ? — user3220407, Jan 28 '14 at 17:50

score 3 · Accepted Answer · answered Jan 28 '14 at 17:57

The ampersand in the foreach-block allows the array to be directly manipulated, since it fetches each value by reference.

$arr = array(1,2,3,4);
foreach($arr as $value) {
    $value *= 2;
}

Each value is multiplied by two in this case, then immediately discarded.

$arr = array(1,2,3,4);
foreach($arr as &$value) {
    $value *= 2;
}

Since this is passed in by reference, each value in the array is actually altered (and thus, $arr becomes array(2,4,6,8))

score 0 · Answer 2 · edited May 23 '17 at 12:31

The ampersand is not unique to PHP and is in fact used in other languages (such as C++). It indicates that you are passing a variable by reference. Just Google "php pass by reference", and everything you need to explain this to you will be there. Some useful links:

http://www.php.net/manual/en/language.references.pass.php
Are PHP Variables passed by value or by reference?
http://www.learncpp.com/cpp-tutorial/73-passing-arguments-by-reference/ (this is for C++, but the same principle applies in PHP)

Ampersand before a variable in foreach php

2 Answers2