(PHP 5 >= 5.2.0, PHP 7, PHP 8)
ArrayObject::ksort — Sort the entries by key
Sorts the entries by key, maintaining key to entry correlations. This is useful mainly for associative arrays.
Note:
If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.
flags
    The optional second parameter flags
    may be used to modify the sorting behavior using these values:
   
Sorting type flags:
SORT_REGULAR - compare items normally;
      the details are described in the comparison operators section
     SORT_NUMERIC - compare items numerically
     SORT_STRING - compare items as strings
     SORT_LOCALE_STRING - compare items as
       strings, based on the current locale. It uses the locale,
       which can be changed using setlocale()
      
     SORT_NATURAL - compare items as strings
       using "natural ordering" like natsort()
      
     SORT_FLAG_CASE - can be combined
       (bitwise OR) with
       SORT_STRING or
       SORT_NATURAL to sort strings case-insensitively
      
     
   Always returns true.
  
Example #1 ArrayObject::ksort() example
<?php
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
$fruitArrayObject = new ArrayObject($fruits);
$fruitArrayObject->ksort();
foreach ($fruitArrayObject as $key => $val) {
    echo "$key = $val\n";
}
 ?>The above example will output:
a = orange b = banana c = apple d = lemon
