I am playing around with arrays in PHP, and I've get confused about unset() function, here's the code:
<?php
$array = array(1, 2, 3, 4);
foreach ($array as $value) {
$value + 10;
}
unset($value);
print_r($array);
?>
Is it necessary to unset($value), when $value remains after foreach loop, is it good practice?
I know this post is old, but I think this info is very important: You asked:
Is it necessary to unset($value), when $value remains after foreach loop, is it good practice?
It depends on wheter you iterate by value or by reference.
$array = array(1, 2, 3, 4);
foreach ($array as $value) {
//here $value is 1, then 2, then 3, then 4
}
//here $value will continue having a value of 4
//but if you change it, nothing happens with your array
$value = 'boom!';
//your array doesn't change.
So it's not necessary to unset $value
$array = array(1, 2, 3, 4);
foreach ($array as &$value) {
//here $value is not a number, but a REFERENCE.
//that means, it will NOT be 1, then 2, then 3, then 4
//$value will be $array[0], then $array[1], etc
}
//here $value it's not 4, it's $array[3], it will remain as a reference
//so, if you change $value, $array[3] will change
$value = 'boom!'; //this will do: $array[3] = 'boom';
print_r ($array); //Array ( [0] => 1 [1] => 2 [2] => 3 [3] => boom! )
So in this case it is a good practice to unset $value, because by doing that, you break the reference to the array. Is it necessary? No, but if you don't do it, you should be very careful.
It can lead to unexpected results like this one:
$letters = array('a', 'b', 'c', 'd');
foreach ($letters as &$item) {}
foreach ($letters as $item) {}
print_r ($letters); //output: Array ( [0] => a [1] => b [2] => c [3] => c )
// [a,b,c,c], not [a,b,c,d]
This is also valid for PHP 7.0
Same code with unset:
$letters = array('a', 'b', 'c', 'd');
foreach ($letters as &$item) {}
unset ($item);
foreach ($letters as $item) {}
print_r ($letters); //output: Array ( [0] => a [1] => b [2] => c [3] => d )
// now it's [a,b,c,d]
I hope this can be useful for someone in the future. :)
There's no need to use unset in the current context that you are using it. unset will simply destroy the variable and its content.
In the example you are giving, this is looping through an array creating $value, then you are unsetting that variable. Which means it no longer exists in that code. So that does absolutely nothing.
To visuallize what I am talking about look at this example:
$value = 'Hello World';
echo $value;
unset($value);
echo $value;
The following out will be:
Hello World<br /><b>NOTICE</b> Undefined variable: value on line number 6<br />
So you will first see the Hello World, but after unsetting that variable trying to call it will just cause an error.
To answer your question, you really don't have to unset value; there's no need for it. As the foreach loop is setting a $value of each array() + 10.
Unsetting it will cause the work to be removed, and forgotten.
unset($value); won't this mess up if you do another foreach using $value later on?
foreach ($array as &$value) { $value + 10; }One reason I can see to unset $value is to make sure you don't unintentionally use it later in the same script. I just had to deal with a really confusing bug caused by duplicating a few lines from inside one loop into another loop, and it used the final value of $value from the first loop. At least if I have unset it I would have got a useful error message due to trying to access a variable that did not exist.
<?php
$array = array(1, 2, 3, 4);
foreach ($array as &$value) {
$value = $value + 10;
}
unset($value);
print_r($array);
you leak the "&", maybe.
foreach ($array as &$value) {it can cause unexpected problems for the unwary, especially if you iterate through that array a second time$value + 10;? is doing nothing