'Undefined' Notice while populating arrays

While populating an array with data from a SimpleXML call, PHP throws exception to what it believes as 'Undefined' keys, however, the output is actually correct.

$doc = new SimpleXmlElement($http_result, LIBXML_NOCDATA);

$result = array();

$x = 0;

foreach($doc->users->user as $item) {
    $result['user'][$x]['id'] .= $item->id;
    $result['user'][$x]['name'] .= $item->name;
    $result['user'][$x]['email'] .= $item->email;
    $x++;
}

print json_encode($result);

This actually outputs what I expect, i.e. {"user":[{"id":"4843977","name":"Test New User","email":"test@开发者_如何学编程newuser.com"}]}

However, the following errors are also present, and I'm not totally sure why - this doesn't appear in 5.2.6 but does for 5.2.10

Notice: Undefined index: user in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined offset: 0 in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: id in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: name in /var/vhosts/sys-dev/docs/file.php on line 37

Notice: Undefined index: email in /var/vhosts/sys-dev/docs/file.php on line 38

Notice: Undefined offset: 1 in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: id in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: name in /var/vhosts/sys-dev/docs/file.php on line 37

Notice: Undefined index: email in /var/vhosts/sys-dev/docs/file.php on line 38

Notice: Undefined offset: 2 in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: id in /var/vhosts/sys-dev/docs/file.php on line 36

Notice: Undefined index: name in /var/vhosts/sys-dev/docs/file.php on line 37

Notice: Undefined index: email in /var/vhosts/sys-dev/docs/file.php on line 38

I think You must change just ".=" to "=" in lines:

$result['user'][$x]['id'] = $item->id;
$result['user'][$x]['name'] = $item->name;
$result['user'][$x]['email'] = $item->email;

You don't define what are $result['user'] and $result['user'][$x]. You need to instantiate them as array so you won't get that error.

$result['user'] = array();
foreach($doc->users->user as $item) {
    $result['user'][$x] = array();
    $x++;
}

For the undefined indexes in the fields, the problem is similar. You use ".=" when the variable doesn't exists yet. So you should instantiate it first with an empty string.

$result['user'][$x]['name'] = '';

You need to initialize the $result array first:

$result = array('user' => array());

And since you’re using the string concatenation and assignment operator .=, that would also apply to the $result['user'][$x] arrays:

foreach($doc->users->user as $item) {
    $result['user'][$x] = array(
        'id'    => null,
        'name'  => null,
        'email' => null
    );
    $result['user'][$x]['id'] .= $item->id;
    $result['user'][$x]['name'] .= $item->name;
    $result['user'][$x]['email'] .= $item->email;
    $x++;
}

But that’s not necessary since you can also write it like this:

$result = array('user' => array());
foreach($doc->users->user as $item) {
    $result['user'][] = array(
        'id'    => $item->id,
        'name'  => $item->name,
        'email' => $item->email
    );
}

Edit    Since we elaborated that the attributes of $item are SimpleXMLElement objects too, $item->attr[0] is required to address the string value itself. Thus:

$result = array('user' => array());
foreach($doc->users->user as $item) {
    $result['user'][] = array(
        'id'    => $item->id[0],
        'name'  => $item->name[0],
        'email' => $item->email[0]
    );
}

It happens, because you're not just setting the array values, but you're concatenating to the current value:

$result['user'][$x]['id'] .= $item->id;

This line means "take the current value of $result['user'][$x]['id'] and add $item->id to it". The notice is then thrown, because the current value is not yet existent.

Amend the code to this

$result['user'][$x]['id'] = $item->id;

and you should be safe. No idea though, why 5.2.6 is not throwing the errors, maybe you should check with the error_reporting setting in the php.ini.