PHP foreach array strange behavior

Question

I have code with two foreach, first with &, second without:

$a = array(1, 2);

foreach ( $a as &$v ) {
    $v *= 1;
}

print_r($a); // output: array(1, 2)

$b = array();

foreach ( $a as $v ) {
    $b[] = $v;
}

print_r($b); // output: array(1, 1)

Why in second foreach $v always = 1 and array b is (1, 1) instead (1, 2)?

Read warning here php.net/manual/en/control-structures.foreach.php — u_mulder
– u_mulder, Commented Jul 4, 2017 at 17:16

SeanJA · Accepted Answer · 2017-07-04 17:30:24Z

You are changing the value of $a[1] in the first loop of the second foreach, if you do a var_dump instead, you get output that indicates it is a reference:

array(2) {
  [0]=>
  int(1)
  [1]=>
  &int(2)
}

So, on the second foreach $a[1] (which is actually &$v; becomes 1), which then is the second value that comes out of $a in the loop, because it is actually:

$a[
   1,
   &$v
];

If you were to reassign $v after the loop, you would get the new value in the array instead:

<?php

$a = [1, 2];
foreach ( $a as &$v ) {
    $v = $v;
}
var_dump($a); // output: array(int(1), &int(2))
$b = [];
foreach ( $a as $v ) {
    $b[] = $v;
}
$v = 3;
var_dump($a); // output: array(int(1), &int(3))

Collectives™ on Stack Overflow

PHP foreach array strange behavior

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related