php - How to get the value of a very specific XML element...?

Solution:

With XPath, you describe what you want to select. Starting form the top of the document at the "root node" with/ and then "walk" down the levels of the tree with each "step".

If you are looking for all of theimportant elements that are children ofsource elements, which are children ofstats:

/stats/source/important
Copy code

Or you could look forimportant elements anywhere, at any level within the document with:

//important
Copy code

And if you only want theimportant element that is a child ofsource with the attributemount="/stu":

/stats/source[@mount="/stu"]/important
Copy code

Applied:

$result = $xml->xpath('/stats/source[@mount="/stu"]/important'); 
foreach ($result as $important){
    echo '/stats/source[@mount="/stu"]/important: ', $important, "\n";
}
Copy code

Solution:

Using DOMDocument & DOMXPath make the task of retrieving particular nodes from within a simple XML file like this quite straightforward.

The XML posted contained errors with thedata tags as mentioned - these were caught bylibxml as it has it's own error handling routines.

$xml='<stats>
        <data1>lorem</data1>
        <data2>ipsum</data2>
        <source mount="/mno">
            <thing>1.0</thing>
            <somethingelse>10</somethingelse>
            <important>12345</important>
            <more>word</more>
        </source>
        <source mount="/pqr">
            <thing>1.0</thing>
            <somethingelse>10</somethingelse>
            <important>23456</important>
            <more>word</more>
        </source>
        <source mount="/stu">
            <thing>1.0</thing>
            <somethingelse>10</somethingelse>
            <important>34567</important>
            <more>word</more>
        </source>
        <source mount="/vwx">
            <thing>1.0</thing>
            <somethingelse>10</somethingelse>
            <important>45678</important>
            <more>word</more>
        </source>
    </stats>';


libxml_use_internal_errors( true ) ;
$dom=new DOMDocument();
$dom->validateOnParse=false;
$dom->recover=true;
$dom->strictErrorChecking=false;
$dom->loadXML( $xml );
$errors=libxml_get_errors();

$xp=new DOMXPath( $dom );
if( $xp ){
    $expr='//source[@mount="/stu"]/important';
    $col=$xp->query( $expr );
    
    if( $col && $col->length > 0 )echo $col->item(0)->nodeValue;
}
Copy code

The XPath expression$expr='//source[@mount="/stu"]/important'; says to find anysource node that has an attributemount that exactly equals the desired string/stu - considerably more complex matching of nodes and attributes can be done than this.

This outputs:

34567
Copy code