Why can't I call property_exists on stdClass?

Question

Here is my code:

<?php

$madeUpObject = new \stdClass();
$madeUpObject->madeUpProperty = "abc";

echo $madeUpObject->madeUpProperty;
echo "<br />";

if (property_exists('stdClass', 'madeUpProperty')) {
    echo "exists";
} else {
    echo "does not exist";
}
?>

And the output is:

abc does not exist

So why does this not work?

Expiratory

Because the made up property isn't defined in stdClass, but $madeUpObject? – Bully

@Pekka웃 Isn't $madeUpObject an instance of stdClass? – Expiratory

Sure, but setting a property on an instance is not going to change the class definition, is it? – Bully

@Pekka웃 When you do not have a property in a class but access $instanceOfThatClass->nonExistingProperty, a public field is generated by php. – Expiratory

Yes but not in the class definition of stdClass – Bully

Answer 1

Try:

if( property_exists($madeUpObject, 'madeUpProperty')) {

Specifying the class name (instead of the object like I have done) means in the stdClass definition, you'd need the property to be defined.

You can see from this demo that it prints:

abc
exists 

Mawson

So $madeUpObject is an instance of class madeUpObject ? – Expiratory

No, it's an instance of stdClass. You're setting a property dynamically (which isn't specified in the class defintion of stdClass). That's why you can't specify the class name as a string to property_exists(). You need to give it the newly created object, since that object is the only thing that has the newly created property. – Mawson

Interesting. So the class does not have the field, but the object does.. Thanks. – Expiratory

I came to this article just to realize that I have been using the call arguments in the wrong order! – Pastorate

Answer 2

Because stdClass does not have any properties. You need to pass in $madeUpObject:

property_exists($madeUpObject, 'madeUpProperty');

The function's prototype is as follows:

bool property_exists ( mixed $class, string $property )

The $class parameter must be the "class name or an object of the class". The $property must be the name of the property.

Gronseth

So madeUpObject is an instance of class madeUpObject? – Expiratory

No it's an instance of stdClass. – Mawson

Answer 3

Unless you're concerned about NULL values, you can keep it simple with isset.

Ovoviviparous