Retieving XML data

I'm using DomDocument to retrieve data from an XML file, my issue that the XML may not have all the data I'm requesting and consequently I'm getting errors along the lines of... Trying to get property of non-object.
I've tried a few workarounds like if isset and if($data=$doc->getElementsByTagName("pcap") but neither seem to be working. I'm not a complete idiot, what am I missing?
Thank is advance for any assistance or suggestions.
worldofwiresAsked:
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Roger BaklundCommented:
>> if $data!=0 then use nodeValue

No, the name of the property is $data->length. You can write just:

if($data->length)

This will be true if length > 0, false if it is 0. In effect it is the same as

if($data->length!=0)

>> is there a problem with constantly reusing the $data value for each getElementByTagName?

No, I don't see any problem with that. On the contrary, it reduces memory consumption.
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Roger BaklundCommented:
>> Trying to get property of non-object.

This would happen when you try to read a property from something that is not an object. For example:

$a=0;
echo $a->b;

Could you post your code and some sample xml?
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worldofwiresAuthor Commented:
Hi, thanks for quick response.

I've included a snippet of the code I'm using and underneath the if statement is an example of what I've been trying to get around the issue. There is a sample xml file attached too, so if the car element for instance doesn't exisit, it would generate the error. I hope this makes sense.

if(file_exists('data/records/xml/'.$fn.'.xml')) {
  $doc = new DOMDocument();
  $doc->load('data/records/xml/'.$fn.'.xml');
 
  $data=$doc->getElementsByTagName("name");
  $arr['name']=array($data->item(0)->getAttribute("last"), $data->item(0)->getAttribute("first"));
 
  $data=$doc->getElementsByTagName("car");
  $arr['car']=$data->item(0)->nodeValue;
}
 
if($data=$doc->getElementsByTagName("car")) $arr['car']=$data->item(0)->nodeValue; else $arr['car']=0;

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sample.xml.txt
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Roger BaklundCommented:
getElementsByTagName() returns a DOMNodeList, this object has a "length" property. Check if this is non-zero before trying to fetch anything from it.
if(file_exists('data/records/xml/'.$fn.'.xml')) {
  $doc = new DOMDocument();
  $doc->load('data/records/xml/'.$fn.'.xml');
 
  $data=$doc->getElementsByTagName("name");
  if($data->length)
    $arr['name']=array($data->item(0)->getAttribute("last"), $data->item(0)->getAttribute("first"));
  else 
    $arr['name']=false;
 
  $data=$doc->getElementsByTagName("car");
  if($data->length)
    $arr['car']=$data->item(0)->nodeValue;
  else 
    $arr['car']=0;
}
 
# The problem with this:
if($data=$doc->getElementsByTagName("car")) 
  $arr['car']=$data->item(0)->nodeValue; else $arr['car']=0;
# ...is that getElementsByTagName() allways returns an object (DOMNodeList), even if no nodes was found.
# Thus, the if-statement is allways true.

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worldofwiresAuthor Commented:
Thanks cxr,

Just to check I've got this, so in my code I can do $data=$doc->getElementsByTagName("car"); And then do an IF statement saying if $data!=0 then use nodeValue, else it's 0?

It seems to work, I'm just clarifying I understand what's going on. Also, in your opinion, is there a problem with constantly reusing the $data value for each getElementByTagName?

Much appreciated.
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Ray PaseurCommented:
This shows how to use SimpleXML to achieve similar results.  I like SimpleXML because I am an inherently simple person ;-)

HTH, ~Ray
<?php // RAY_xml_example_24.php
error_reporting(E_ALL);
echo "<pre>\n"; // READABILITY
 
 
 
// TEST DATA FROM THE ORIGINAL POST USING HEREDOC SYNTAX
// MAN PAGE http://www.tuxradar.com/practicalphp/2/6/3
$xml = <<<MYXML
<?xml version="1.0"?>
<record>
  <effective>2009-01-26</effective>
  <generated_date>2009-01-05 11:48:06</generated_date>
  <generated_by>13</generated_by>
  <reason code="OFFERV2" title="Offer to Employee v2" id="10"/>
  <parent code="LEGAL AMEA" title="Chief Counsel, AMEA Region" id="25"/>
  <name first="Mickey" last="Mouse"/>
  <hypo allowance="6035" deduction="2531.25" total="3503.75" code="350L"/>
  <car>1</car>
</record>
MYXML;
 
 
 
// MAKE AN OBJECT
$obj = SimpleXML_Load_String($xml);
var_dump($obj);
 
// ACCESS THE DATA TO SIMULATE SOME PROCESSING ROUTINES
$arr = array();
 
// GET THE NAME FROM THE ATTRIBUTES OF AN XML TAG
$arr["name"] = $obj->name["first"] . ' ' . $obj->name["last"];
// GET A FIELD THAT DOES NOT EXIST
$arr["foo"]  = (bool)   $obj->foo;
// GET AN ELEMENT FROM WITHIN THE XML TAG
$arr["car"]  = (string) $obj->car;
 
// VISUALIZE THE DATA
var_dump($arr);

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worldofwiresAuthor Commented:
Thanks both,

I've used the SimpleXML on another XML function but got a little lost when using attributes. I like to keep things simple. :) I may rewrite but in teh meantime, xcr has solved my error generating problem.

Excellent, thaks guys. This site rocks.
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Ray PaseurCommented:
Thanks for the points.  The rule of attributes is that they are array indexes.  See line 33 of the post above for the way to isolate those.  Best regards, ~Ray
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