CODEWITHSUNDEEP
phpforeach
Thanh Trung
Thanh Trung

Reputation: 3804

php removing elements inside foreach

$array = array('1','3','20','10');
foreach ($array as $i=>$arr) {
   if ($i==0) unset($array[$i]);
}

Question: would removing one element mess up the order of the iteration of this loop? What happen when I remove the element with the index smaller/equal/bigger than the current iterating index?

What should I avoid to do when modifying the original array while iterating over it?

Edit: In case the array is passed by reference?

Upvotes: 0

Views: 169

Answers (2)

Passerby
Passerby

Reputation: 10080

Particularly to your provided code, once

$array = array('1','3','20','10');

is declared, the keys are bound, so

if($i==0) unset($array[$i]);

will only unset '1', and you will be left with

array(2) {
  [1]=>
  string(1) "2"
  [2]=>
  string(1) "3"
}

And as @cleong said, PHP seems to create a copy of the array when iterating:

$arr=array("1","2","3");
foreach($arr as $idx=>$val)
{
    if(isset($arr[1])) unset($arr[1]);
    echo $val."\n";
}
var_dump($arr);

will return

1
2
3
array(2) {
  [0]=>
  string(1) "1"
  [2]=>
  string(1) "3"
}

So it's "OK" to unset elements inside an iteration, as long as the unset would not generate error (e.g. unsetting an already unset variable).

But, I don't think this is a good idea. If your question is "how to avoid this", provide an example of why you have to do this.

Upvotes: 1

cleong
cleong

Reputation: 7626

PHP creates a copy of the array when you use a foreach loop(). Even if you blow away the array entirely, the iteration will continue as through nothing has happened. To wit:

$array = array("a", "b", "c");

foreach($array as $element) {
    $array = null;
    echo "$element ";
}

Output:

a b c

Upvotes: 0

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