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php – change initial array inside the foreach loop?

Posted by: admin April 23, 2020 Leave a comment

Questions:

i want to have a foreach loop where the initial array is changed inside the loop.

eg.

$array = array('red', 'blue');
foreach($array as $key => $value) {
    $array[] = 'white';
    echo $value . '<br />';
}

in this loop the loop will print out red and blue although i add another element inside the loop.

is there any way to change the initial array inside the loop so new elements will be added and the foreach will use the new array whatever is changed?

i need this kind of logic for a specific task:

i will have a if statement that search for a link. if that link exists, it is added to the array. the link content will be fetched to be examined if it contains another link. if so, this link is added, and the content will be fetched, so on so forth.. when no link is further founded, the foreach loop will exit

How to&Answers:

I don’t think this is possible with a foreach loop, at least the way you wrote it : doesn’t seem to just be the way foreach works ; quoting the manual page of foreach :

Note: Unless the array is referenced, foreach operates on a copy
of the specified array and not the
array itself.

Edit : after thinking a bit about that note, it is actually possible, and here’s the solution :

The note says “Unless the array is referenced” ; which means this portion of code should work :

$i = 0;
$array = array('red', 'blue');
foreach($array as $key => & $value) {
    $array[] = 'white';
    echo $value . '<br />';
    if ($i++ >= 5) {
        break;   // security measure to ensure non-endless loop
    }
}

Note the & before $value.

And it actually displays :

red
blue
white
white
white
white

Which means adding that & is actually the solution you were looking for, to modify the array from inside the foreach loop 😉

Edit : and here is the solution I proposed before thinking about that note :

You could do that using a while loop, doing a bit more work “by hand” ; for instance :

$i = 0;

$array = array('red', 'blue');

$value = reset($array);
while ($value) {
    $array[] = 'white';
    echo $value . '<br />';
    if ($i++ >= 5) {
        break;   // security measure to ensure non-endless loop
    }
    $value = next($array);
}

Will get you this output :

red
blue
white
white
white
white

Answer:

What you need to do is move the assignment inside the for loop and check the length of the array every iteration.

$array = array('red', 'blue');
for($i = 0; $i < count($array); $i++)
{
   $value = $array[$i];
   array_push($array, 'white');
   echo $value . '<br />';
}

Be careful, this will cause an infinite loop (white will be added to the end of the array at every loop).

Answer:

Maybe you should use some other way, like:

$ar = array('blue', 'red');
while ($a = array_pop($ar) {
     array_push($ar, 'white');
}

Or something like this…

Answer:

You can access the array by using the $key

$array = array('red', 'blue');
foreach($array as $key => $value) {
    $array[$key] = 'white';
}

Answer:

In order to be able to directly modify array elements within the loop
precede $value with &. In that case the value will be assigned by
reference. [source]

All you have to do to your old code is

precede $value with &

like so

$array = array('red', 'blue');
foreach($array as $key => &$value) {// <-- here
    $array[] = 'white';
    echo $value . '<br />';
}

A while loop would be a better solution.

while (list ($key, $value) = each ($array) ) {
    $array[] = 'white';
    echo $value . '<br />';
}

If you don’t need the $key variable, as your example suggests then using $value = array_pop($array) instead if list ($key, $value) = each ($array) would be a less expensive option. see @enrico-carlesso’s Answer Here

As your array is sequantial(numeric,indexed) and not associative then you could use a for loop instead.

for ($key = 0; $key < count($array); ++$key) {
    $value = $array[$i];

    $array[] = 'white';
    echo $value . '<br />';
}

As a side note.

I don’t understand why its &$value and not &array.

&$value would suggest you can only modify the current element within the loop.
&array would suggest you could modify all array elements within the loop, including adding/removing element.