Trying to loop through array and reassign value

Question

I have two arrays, both with the same indexes. What I want to do is loop through one of the arrays (portConfigArray), and change the value of an existing item by using data from a second array. (portStatusArray) Here's the logic:

$i=0;
foreach ($portConfigArray as $configentry)
{           
    $configentry['LinkState'] = $portStatusArray[$i]['LinkState'];
    $i = $i + 1;
    echo $configentry['LinkState'];             
}
$portdetailsArray = $portConfigArray;
var_dump($portdetailsArray);

the echo statement shows the correct values being assigned for each item in the portConfigArray. (its just a string value like "Up" or "Down") But in the var_dump I can see that the value hasn't been updated correctly. It shows

["LinkState"]=> string(0) ""

as the output for each record.

Can you tell me what I'm doing wrong?

Jonnix · Accepted Answer · 2012-12-06 16:57:53Z

1

You need to make $configentry a reference, otherwise it's just a copy

foreach ($portConfigArray as &$configentry)

answered Dec 6, 2012 at 16:57

Jonnix

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2 Comments

Marc B Over a year ago

This can blow up on you, because $configentry will STAY a reference until you unset() it, or the script ends. If you reuse $configentry later in the script, you'll be changing the LAST element you foreach'd on, which can cause serious confusion.

Jonnix Over a year ago

Agreed. You should always be diligent when using references.

cowls · Accepted Answer · 2012-12-06 16:57:48Z

1

foreach ($portConfigArray as $configentry)

Should be

foreach ($portConfigArray as &$configentry)

Essentially this means the loop deals with the actual value rather than a copy of it.

answered Dec 6, 2012 at 16:57

cowls

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Comments

Marc B · Accepted Answer · 2012-12-06 17:03:05Z

While you can make $configentry a reference, as stated in other answers, it CAN cause major issues if you reuse such "referenced" variables later on in the script for other purposes. A safer method is to use the key=>val version of foreach, and directly modify the array:

foreach($portConfigArray as $key => $configentry) {
    $portConfigArray[$key] = 'newvalue';
}

The reference version can cause issues, e.g.

php > $a = array('a', 'b', 'c');
php > foreach($a as &$val) { $val++; };
php > print_r($a);
Array
(
    [0] => b
    [1] => c
    [2] => d
)
php > $b = array('p', 'q', 'r');
php > foreach($b as $val) { $val++; };  <--note, $val, not &$val
php > print_r($b);
Array
(
    [0] => p   <---hey, these 3 didn't change!
    [1] => q
    [2] => r
)
php > print_r($a);
Array
(
    [0] => b
    [1] => c
    [2] => s  <---uh-oh!
)
php >

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