xml - PHP simplexmlelement fails to find attribute when attribute path is assigned to variable

Question

My code parses an array to get the paths to various attributes in an xml file. I load the xml as a simplexmlelement like so:

$xml = simplexml_load_string($xml_string);
$address = $xml->response->addressinformation->records->record[0];

This code will work and displays the correct value of '03':

$from = $address->{'from-date'}['month'];
echo $from;

//prints '03'

The {} around from-date are necessary because of the - in the element name.

The following code blocks seem like they should be functionally equivalent to the above code, but when I assign the path to a $variable it does not work.

$path = "{'from-date'}['month']";
$from = $address->$path;
echo $from;

//prints ''

$path = "from-date['month']";
$from = $address->$path;
echo $from;

//prints ''

This code will work.

//normal path
$from = $address->{'from-date'};

//path assigned to variable
$path = "from-date";
$from2 = $address->$path;

var_dump($from);
var_dump($from2);

//both correctly output - object(SimpleXMLElement)#1587 (1) 
//{ ["@attributes"]=> array(2) { ["year"]=> string(4) "2003" ["month"]=> string(2) "03" } }

It only seems to fail when I target the specific attribute with ['month']. I know the answer to this question is just going to be some silly thing that I'm doing wrong. Can anyone tell me what it is?

Sample XML

$xml_string = '
<?xml version="1.0" encoding="utf-8"?>
<root>
    <response>
        <addressinformation>
            <records>
                <record id="1">
                    <fullname>JOHN E DOE</fullname>
                    <firstname>JOHN</firstname>
                    <middlename>E</middlename>
                    <lastname>DOE</lastname>
                    <fulldob>01/01/1970</fulldob>
                    <from-date year="2003" month="03"/>
                    <to-date year="2010" month="09"/>
                </record>
                <record id="2">
                    <fullname>JOHN E DOE</fullname>
                    <firstname>JOHN</firstname>
                    <from-date year="2003" month="03"/>
                    <to-date year="2010" month="09"/>
                </record>
            </records>
        </addressinformation>
        <otherinformation>
            <records>
                <record id="3">
                    <fullname>JOHN DOE</fullname>
                    <firstname>JOHN</firstname>
                    <lastname>DOE</lastname>
                    <fulldob>01/01/1970</fulldob>
                </record>
                <record id="4">
                    <fullname>JOHN EDWARD DOE</fullname>
                    <firstname>JOHN</firstname>
                    <middlename>EDWARD</middlename>
                    <lastname>DOE</lastname>
                    <fulldob>19700000</fulldob>
                </record>
                <record id="5">
                    <fullname>JOHN EDWARD DOE</fullname>
                    <firstname>JOHN</firstname>
                    <middlename>EDWARD</middlename>
                    <lastname>DOE</lastname>
                    <fulldob>19830000</fulldob>
                </record>
            </records>
        </otherinformation>
    </response>
</root>
';

question from:https://stackoverflow.com/questions/65914698/php-simplexmlelement-fails-to-find-attribute-when-attribute-path-is-assigned-to

Answer 1

What you're trying to do is not possible; you can only use a variable for the name of the property you are trying to access, not to then reference that as an array. When you try to use

$path = "{'from-date'}['month']";
$from = $address->$path;

you are actually trying to access an object property whose name is {'from-date'}['month'], which is why you get no result.

What you could do is specify the attribute using a variable as well:

$path = "from-date";
$attr = 'month';
$from2 = $address->$path[$attr];
echo $from2;

which will output

03

as desired.