PHP "&" operator

I'm not a PHP programmer (but know other languages), and I'm trying to understand a web page that was done in PHP (5.1.6) in order to do some changes.

The page has the following code (simplified):

$db_hosts = array();
$sql = 'SELECT h.hostid, h.host FROM hosts h ';

$db_items = DBselect($sql);

while($db_item = DBfetch($db_items)){
    $name = $db_item['host'];
    $db_host = &$db_hosts[$db_item['hostid']];

}

I'm trying to understand the last line, $db_host = &$db_hosts[$db_item['hostid']];.

It seems to be creating a new variable, $db_host, and putting something inside it, but I don't understand &$db_hosts.

I'm in doubt because as far as I know, $db_hosts is an empty array.

I found this and this, but I'm not quite sure, because in these links, the operator is "=&", and in the code, the operator is attached to the variable "= &$db_hosts" (it has an space between = and &).

Since I tried to modify it and didn't get success, I thought that it was better to ask for help...

Answer

Those are references, and they are similar to "pointers" in C or C++.

More information is in the PHP manual.

In this case, since $db_hosts is empty, the construct $db_hosts[$db_item['hostid']] will create a new array with an empty item on the index of $db_item['hostid'] and return the item's reference, making $db_host act as an 'alias' for whatever $db_hosts[$db_item['hostid']] is currently.