iterating over the same array twice, first by reference and then by value seems to alter the original array

[aliber4079]

Description

The following code:

<?php
$criteria=[
        "a",
        "b",
];
var_dump($criteria);
foreach ($criteria as &$criterion) {
}
foreach ($criteria as /*&*/$criterion){
}                              
var_dump($criteria);

Resulted in this output:

array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
}
array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  &string(1) "a"
}

But I expected this output instead:

array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
}
array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  &string(1) "b"
}

PHP Version

PHP 8.5.3 (cli) (built: Feb 10 2026 18:44:09) (ZTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Built by The PHP Group
Zend Engine v4.5.3, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.3, Copyright (c), by Zend Technologies

Operating System

windows x64

[alecpl]

This is interesting. If you change the variable name in the first loop e.g. foreach ($criteria as &$c) {} the result is different.
Also if you remove the second loop the second array element is still reported as a reference, but with a correct value this time.

It's the same on all PHP versions (with small reference difference in PHP 5.0-5.2).

[iluuu1994]

Hi @aliber4079. There are too many duplicates of this to keep track at this point. Check the big red warning on this page:

https://www.php.net/manual/en/control-structures.foreach.php

Warning Reference to a $value of the last array element remain even after the foreach loop. It is recommended to destroy these using unset(). Otherwise, the following behavior will occur:

 $arr = [1, 2, 3, 4];
 foreach ($arr as &$value) {
     $value = $value * 2;
 }
 // $arr is now [2, 4, 6, 8]
 
 // without an unset($value), $value is still a reference to the last item: $arr[3]
 
 foreach ($arr as $key => $value) {
     // $arr[3] will be updated with each value from $arr...
     echo "{$key} => {$value} ";
     print_r($arr);
 }
 // ...until ultimately the second-to-last value is copied onto the last value

The above example will output:

 0 => 2 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 2 )
 1 => 4 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 4 )
 2 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )
 3 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )