Why can't I access elements inside an XML file with XPath in XML::LibXML?

I have an XML file, part of which looks like this:

 <wave waveID="1">
    <well wellID="1" wellName="A1">
 开发者_如何学Go     <oneDataSet>
        <rawData>0.1123975676</rawData>
      </oneDataSet>
    </well>
    ... more wellID's and rawData continues here...

I am trying to parse the file with Perl's libXML and output the wellName and the rawData using the following:

    use XML::LibXML;
    my $parser = XML::LibXML->new();
    my $doc = $parser->parse_file('/Users/johncumbers/Temp/1_12-18-09-111823.orig.xml');
    my $xc = XML::LibXML::XPathContext->new( $doc->documentElement()  );
    $xc->registerNs('ns', 'http://moleculardevices.com/microplateML');

            my @n = $xc->findnodes('//ns:wave[@waveID="1"]');   #xc is xpathContent
        # should find a tree from the node representing everything beneath the waveID 1
        foreach $nod (@n) {
            my @c = $nod->findnodes('//rawData');  #element inside the tree.
            print @c;
        }

It is not printing out anything right now and I think I have a problem with my Xpath statements. Please can you help me fix it, or can you show me how to trouble shoot the xpath statements? Thanks.

Instead of using findnodes in the loop, use getElementsByTagName():

my @c = $nod->getElementsByTagName('rawData');

Here are some other handy methods to use processing to @c array:

$c[0]->toString;    # <rawData>0.1123975676</rawData>
$c[0]->nodeName;    # rawData
$c[0]->textContent; # 0.1123975676

If the 'wave' element is in a namespace then the 'rawData' element is as well so you probably need to use

foreach $nod (@n) {
    my @c = $xc->findnodes('descendant::ns:rawData', $nod);  #element inside the tree.
    print @c;
}