Description:
------------
We use this array:
array(2) { [1]=>  int(100) [2]=>  int(200) }

When a array will be encoded into a json string, php converts integer indexes t o strings:
string(17) "{"1":100,"2":200}"

When php decodes the json string back, it will be an object:
object(stdClass)#1 (2) { ["1"]=>  int(100) ["2"]=>  int(200) }

To avoid the problem that you not can acces integer indexes of a object you must cast the object to an array:
array(2) { ["1"]=>  int(100) ["2"]=>  int(200) }

Now the indexes become strings instead of integers, which you cannot access:
$arr2[1] = NULL


The json_decode function should convert indexes back to integer, if they are a string number, like php always does when you create an array.


Test script:
---------------
$arr = array(1=>100,2=>200,"1"=>100,"2"=>200);
$json = json_encode($arr);
$arr2 = (array)json_decode($json);
	
var_dump($arr2);
var_dump($arr2[1]);
var_dump($arr2["1"]);

Expected result:
----------------
array(4) {
  [1]=>
  int(100)
  [2]=>
  int(200)
}
int(100)
int(100)


Actual result:
--------------
array(4) {
  ["1"]=>
  int(100)
  ["2"]=>
  int(200)
}
NULL
NULL