$value versus &$value in foreach

[andrewteg]

What is the difference between these two lines of code. I know in the second I added a & but what does that do exactly?

[PHP]foreach ($arr as $value)[/PHP]

[PHP]foreach ($arr as &$value)[/PHP]

Thanks,
Andrew

[theS70RM]

What is the difference between these two lines of code. I know in the second I added a & but what does that do exactly?

[PHP]foreach ($arr as $value)[/PHP]

[PHP]foreach ($arr as &$value)[/PHP]

Thanks,
Andrew

is the difference that one of them creates a parse error? =P

as far as i know (and i am no expert) the & does nothing and is incorrect syntax.


Andy

[Markus]

is the difference that one of them creates a parse error? =P

as far as i know (and i am no expert) the & does nothing and is incorrect syntax.


Andy

I'm not sure; i've seen it used in other scripts.

Never known what it was for though.

Be useful to get some insight though :)

Regards.

[theS70RM]

check this

http://www.litfuel.net/plush/?postid=8


an addition to php5 it would seem.

pointers, references etc just confuse me, thats why i leave C alone ;)


Andy

[andrewteg]

I know they are both valid. I did a foreach with the & and it changed the value of my variable but without it it did not!

I have seen the code on www.php.net and actually just found this on http://www.php.net/foreach

As of PHP 5, you can easily modify array's elements by preceding $value with &. This will assign reference instead of copying the value.

So it's a PHP5 thing that passes by reference and can modify your variable.

Uses & so changes $arr
[PHP]
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
$value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
[/PHP]
No & so no change to $arr
[PHP]
$arr = array(1, 2, 3, 4);
foreach ($arr as $value) {
$value = $value * 2;
}
// $arr is still array(1, 2, 3, 4)
[/PHP]

[Markus]

I know they are both valid. I did a foreach with the & and it changed the value of my variable but without it it did not!

I have seen the code on www.php.net and actually just found this on http://www.php.net/foreach

So it's a PHP5 thing that passes by reference and can modify your variable.

Uses & so changes $arr
[PHP]
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
$value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
[/PHP]
No & so no change to $arr
[PHP]
$arr = array(1, 2, 3, 4);
foreach ($arr as $value) {
$value = $value * 2;
}
// $arr is still array(1, 2, 3, 4)
[/PHP]

Ahhhh, useful!

Regards

[TheServant]

Good question. I didn't even know the "FOREACH construct used to loop through PHP arrays works on a COPY of the array and not the array itself" so I will definately be using this in the future.

[ronverdonk]

For your information: there is quite a good explanation about passing values by pointer and by reference in the PHP documentation in chapter References Explained

Ronald

[Atli]

Good question. I didn't even know the "FOREACH construct used to loop through PHP arrays works on a COPY of the array and not the array itself" so I will definately be using this in the future.

Be careful tho.
As explained in one of the links posted above, even tho the old un-referenced foreach is in fact working on a copy of the array, the internal PHP engine still references the original array until you actually modify the copy.

In the end, referencing the array will trigger internal safe-guards that may cause your code to run slower.

So, only use the referenced version if you plan on actually changing the original data while iterating through it.

[TheServant]

Be careful tho.
As explained in one of the links posted above, even tho the old un-referenced foreach is in fact working on a copy of the array, the internal PHP engine still references the original array until you actually modify the copy.

In the end, referencing the array will trigger internal safe-guards that may cause your code to run slower.

So, only use the referenced version if you plan on actually changing the original data while iterating through it.

Good point, I will definately do that. Thanks.