XPath根据属性值定位元素？

As Micheal Kay has outlined in his answer, the xpath expression is valid. What he does not know is that for SimpleXML this won't lead into an empty result.

So you see a fatal error as you try to read a field from an empty array. Your code works similar to this one:

$found = array();
echo $found->state;

Which echoes an empty string (created out of the NULL value that expression give) and a notice:

Notice: Trying to get property of non-object in ...

If you don't see yet this notice, it's crucial you enable error messages with your development system, see How to get useful error messages in PHP?.

So as you can see, it is working properly, it just does not provide what you expect. To go on with that in a more productive manner for yourself, it would have been great if you would have shared what exactly you did expect instead.

Or in other words: As others have answered as well, you need to decide what you're looking for.

From the output code:

echo $found->state;

I'd say you're looking for the following XML element:

...
<repstate location="AK">
    <compName>Test Company</compName>
    <name>Chris Brown</name>
    <address>123 Main St</address>
    <city>Anytown</city>
    <state>CT</state>
    ...

So here is how SimpleXML Xpath works:

1. you can only query lists of nodes
2. the only nodes supported are elements and attributes
3. the list is always of type array
4. the array is always zero-indexed
5. each entry in the array - if the array is not empty - is of type SimpleXMLElement

So in your case if my assumption of the element to query you expect to get is correct, you want the state child-element's node value of a single element node returned. The according PHP code then would be:

$list = $xml->xpath("//repstate[@location = 'AK']");
list($repstate) = $list + array(null);
$state = $repstate ? $repstate->state : '- no such location -';

echo $state;

The output with your XML then would be:

CT

Or even shorter:

$list = $xml->xpath("//repstate[@location = 'AK']/state");
list($state) = $list + array('- no such location -');

echo $state;

I hope this more expansive explanation is helpful for you. The reason why your original expression does not work is that it's already violating the first point:

1. you can only query lists of nodes

because your xpath query represented a boolean expression and not a node-list. Additionally such a list in SimpleXMLElement xpath would need you to have an element or attribute and not a boolean expression.

I am not 100% positive on this, but in c# the xPath would be:
//repstate[@location='AK']
so you can try that (I can't put that in a comment as I don't have a high enough reputation :))

You haven't said what you want your XPath expression to do. Your expression is valid, it will return a boolean which will be true if there is an @location attribute equal to "AK" anywhere in the document.

If you want to find the element that has an @location attribute equal to "AK", use //*[@location='AK'].

In addition to the xpath-expression itself, xpath will return an array of SimpleXML elements to $found, so...

echo $found[0]->state;

or - with PHP >= 5.4 - you can de-reference the array like this:

$found = $xml->xpath(...)[0];
echo $found->state;

see it here: https://eval.in/435965