PHP return value after XML exploration - php

Question

I got a PHP array with a lot of XML users-file URL :
$tab_users[0]=john.xml
$tab_users[1]=chris.xml
$tab_users[n...]=phil.xml
For each user a <zoom> tag is filled or not, depending if user filled it up or not:
john.xml = <zoom>Some content here</zoom>
chris.xml = <zoom/>
phil.xml = <zoom/>
I'm trying to explore the users datas and display the first filled <zoom> tag, but randomized: each time you reload the page the <div id="zoom"> content is different.
$rand=rand(0,$n); // $n is the number of users
$datas_zoom=zoom($n,$rand);
My PHP function
function zoom($n,$rand) {
global $tab_users;
$datas_user=new SimpleXMLElement($tab_users[$rand],null,true);
$tag=$datas_user->xpath('/user');
//if zoom found
if($tag[0]->zoom !='') {
$txt_zoom=$tag[0]->zoom;
}
... some other taff here
// no "zoom" value found
if ($txt_zoom =='') {
echo 'RAND='.$rand.' XML='.$tab_users[$rand].'<br />';
$datas_zoom=zoom($r,$n,$rand); } // random zoom fct again and again till...
}
else {
echo 'ZOOM='.$txt_zoom.'<br />';
return $txt_zoom; // we got it!
}
}
echo '<br />Return='.$datas_zoom;
The prob is: when by chance the first XML explored contains a "zoom" information the function returns it, but if not nothing returns... An exemple of results when the first one is by chance the good one:
// for RAND=0, XML=john.xml
ZOOM=Anything here
Return=Some content here // we're lucky
Unlucky:
RAND=1 XML=chris.xml
RAND=2 XML=phil.xml
// the for RAND=0 and XML=john.xml
ZOOM=Anything here
// content founded but Return is empty
Return=
What's wrong?

Answer 1

I suggest importing the values into a database table, generating a single local file or something like that. So that you don't have to open and parse all the XML files for each request.
Reading multiple files is a lot slower then reading a single file. And using a database even the random logic can be moved to SQL.
You're are currently using SimpleXML, but fetching a single value from an XML document is actually easier with DOM. SimpleXMLElement::xpath() only supports Xpath expression that return a node list, but DOMXpath::evaluate() can return the scalar value directly:
$document = new DOMDocument();
$document->load($xmlFile);
$xpath = new DOMXpath($document);
$zoomValue = $xpath->evaluate('string(//zoom[1])');
//zoom[1] will fetch the first zoom element node in a node list. Casting the list into a string will return the text content of the first node or an empty string if the list was empty (no node found).
For the sake of this example assume that you generated an XML like this
<zooms>
<zoom user="u1">z1</zoom>
<zoom user="u2">z2</zoom>
</zooms>
In this case you can use Xpath to fetch all zoom nodes and get a random node from the list.
$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new DOMXpath($document);
$zooms = $xpath->evaluate('//zoom');
$zoom = $zooms->item(mt_rand(0, $zooms->length - 1));
var_dump(
[
'user' => $zoom->getAttribute('user'),
'zoom' => $zoom->textContent
]
);

Answer 2

Your main issue is that you are not returning any value when there is no zoom found.
$datas_zoom=zoom($r,$n,$rand); // no return keyword here!
When you're using recursion, you usually want to "chain" return values on and on, till you find the one you need. $datas_zoom is not a global variable and it will not "leak out" outside of your function. Please read the php's variable scope documentation for more info.
Then again, you're calling zoom function with three arguments ($r,$n,$rand) while the function can only handle two ($n and $rand). Also the $r is undiefined, $n is not used at all and you are most likely trying to use the same $rand value again and again, which obviously cannot work.
Also note that there are too many closing braces in your code.
I think the best approach for your problem will be to shuffle the array and then to use it like FIFO without recursion (which should be slightly faster):
function zoom($tab_users) {
// shuffle an array once
shuffle($tab_users);
// init variable
$txt_zoom = null;
// repeat until zoom is found or there
// are no more elements in array
do {
$rand = array_pop($tab_users);
$datas_user = new SimpleXMLElement($rand, null, true);
$tag=$datas_user->xpath('/user');
//if zoom found
if($tag[0]->zoom !='') {
$txt_zoom=$tag[0]->zoom;
}
} while(!$txt_zoom && !empty($tab_users));
return $txt_zoom;
}
$datas_zoom = zoom($tab_users); // your zoom is here!
Please read more about php scopes, php functions and recursion.

Answer 3

There's no reason for recursion. A simple loop would do.
$datas_user=new SimpleXMLElement($tab_users[$rand],null,true);
$tag=$datas_user->xpath('/user');
$max = $tag->length;
while(true) {
$test_index = rand(0, $max);
if ($tag[$test_index]->zoom != "") {
break;
}
}
Of course, you might want to add a bit more logic to handle the case where NO zooms have text set, in which case the above would be an infinite loop.