Next key in array

$next = next($array); 
echo key($array);

Should return the key corresponding to $next;

next($array);
$key = key($array);
prev($array);

If pointer is not on this element, as other solutions assume, You can use

<?php
    $keys = array_keys($arr);
    print $keys[array_search("gsda",$keys)+1];

Update: Note that this is not a valid answer, as it's searching for values instead of keys.

---

If the pointer of current() is on the right key, @Thomas_Cantonnet is right and you want to use next(). If you did not iterate through the array via next(), you first have to go through the array to set the internal index pointer correctly:

$search = "bsdf";
while (($next = next($array)) !== NULL) {
    if ($next == $search) {
        break;
    }
}

Now $next points to your current search-index and you can iterate over the rest via next().