PHP array unset() behavior - last array key remains?

Question

I have an array constructed out of several strings (HTTP addresses) on which I run a PHP Filter and the unset() method to remove non-valid URLs. However, the last array item is never removed - and I don't know why, or how I solve this. I'm hoping you guys can help.

$url1 = "http://localhost/work/project/scrapes/1.html";
$url2 = "";
$url3 = "";

$urls = array($url1, $url2, $url3);

for($x = 0; $x < sizeof($urls); $x++){
    if(!filter_var($urls[$x], FILTER_VALIDATE_URL)){
        unset($urls[$x]);
    }
}

print_r() gives me this:

Array ( [0] => http://localhost/work/project/scrapes/1.html [2] => )

I have no idea why $urls[2] is still there, and why it's not removed.

Answer 1

Because you calculate the size() dynamically - it reduces as long as you delete elements. So the fix is to get the size before the loop:

$url1 = "http://localhost/work/project/scrapes/1.html";
$url2 = "";
$url3 = "";

$urls = array($url1, $url2, $url3);
$size = sizeof($urls); // <----

for($x = 0; $x < $size; $x++){
    if(!filter_var($urls[$x], FILTER_VALIDATE_URL)){
        unset($urls[$x]);
    }
}

var_dump($urls);

Answer 2

That is because you are calculating the size of the array in each iteration.

By Iteration:

1. sizeof($urls) = 3, $x = 0, $x < sizeof($urls) TRUE unset($urls[0]);

2. sizeof($urls) = 2, $x = 1, $x < sizeof($urls) TRUE unset($urls[1]);

3. sizeof($urls) = 1, $x = 2, $x < sizeof($urls) FALSE ... no more code executed

save the length of the array before start the loop

$length = sizeof($urls);

for($x = 0; $x < $length; $x++){
}