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?

Because the made up property isn't defined in `stdClass`, but `$madeUpObject`? — Pekka, Feb 01 '13 at 21:07
Sure, but setting a property on an instance is not going to change the class definition, is it? — Pekka, Feb 01 '13 at 21:09
@Pekka웃 When you do not have a property in a class but access $instanceOfThatClass->nonExistingProperty, a public field is generated by php. — Koray Tugay, Feb 01 '13 at 21:14

score 14 · Accepted Answer · answered Feb 01 '13 at 21:09

14

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

answered Feb 01 '13 at 21:09

nickb

59,313
13
108
143

So $madeUpObject is an instance of class madeUpObject ? – Koray Tugay Feb 01 '13 at 21:12
1

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. – nickb Feb 01 '13 at 21:14
Interesting. So the class does not have the field, but the object does.. Thanks. – Koray Tugay Feb 01 '13 at 21:15
I came to this article just to realize that I have been using the call arguments in the wrong order! – Adam Fowler Jan 26 '17 at 21:34

Sverri M. Olsen · Answer 2 · 2013-02-01T21:16:57.557

5

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.

edited Feb 01 '13 at 21:16

answered Feb 01 '13 at 21:09

Sverri M. Olsen

13,055
3
36
52

So madeUpObject is an instance of class madeUpObject? – Koray Tugay Feb 01 '13 at 21:11
No it's an instance of `stdClass`. – nickb Feb 01 '13 at 21:11

score 2 · Answer 3 · answered Feb 01 '13 at 21:11

2

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

answered Feb 01 '13 at 21:11

Martin

6,632
4
25
28

Why can't I call property_exists on stdClass?

3 Answers3