PHP: Using $_GET["id"] to replace XML node - php

Question

I am using PHP and an external XML file to display an HTML page which allows a user to update an item's status using various form/input buttons.
The current format is that you can look at one HTML page with a master list of items and their status, then click on one to move to a new HTML page letting you specify the status of that item. So I can click on "Widget X", then see a new page (status.php?id=X), then click on a button labeled "ready", and PHP will use $_GET["id"] to find the relevant XML node and replace it's attribute with "ready".
For some reason I absolutely cannot get PHP to use the data from $_GET to specify an XML node. Here is the current troubleshooting code:
<?php
$idx = $_GET["id"]; /*Get id# from previous page*/
$xml = simplexml_load_file('test.xml'); /*Load external .xml*/
$array = array(100, 200, 300); /*Basic array for comparison*/
print_r($xml); /*Display contents of test.xml*/
$xml->item[$idx]->status = 'waiting'; /*change item $idx's status to 'waiting'*/
echo '<br/>';
print_r($xml); /*Display changed xml*/
/*Display changed basic array values to confirm $idx has a value*/
$array[$idx] = 123;
echo '<br/>';
print_r($array);
$array["$idx"] = 456;
echo '<br/>';
print_r($array);
$array["{$idx}"] = 789;
echo '<br/>';
print_r($array);
?>
And here is the contents of test.xml:
<?xml version="1.0" standalone="yes"?>
<widgets>
<item>
<name>Widget X</name>
<status>ready</status>
</item>
<item>
<name>Widget Z</name>
<status>waiting</status>
</item>
</widgets>
The basic array has no problem using $idx = $_GET["id"]; to choose which array element to change. But $xml->item[$idx]->status does not work. If, however, I change to $idx = 0, then $xml->item[$idx]->status does work.
Is this a bug, or am I missing something about how $_GET or SimpleXML works?

Answer 1

Accessing nth element of XML in PHP with SimpleXml
It seems SimpleXML distinguishes between numeric and non-numeric array
offsets in a slightly different way to a normal PHP array, so you need
to cast your variable to an integer first. (All input from the query
string is a string until you tell PHP otherwise.)
$var = intval($_GET['var']); echo $xml->foo[$var]->bar; This will turn
the string '1' into the integer 1, and should give the result you
require.