No Error for Undefined Variable Used in Class Methods in PHP

Question

I spent more than 10 hours to find out the typo for debugging my PHP program. I expected PHP would produce an error when using an undefined variable. But when it is used as an object in a method, it doesn't. Is there a reason for it?

<?php

    $oClass = new MyClass;
    // $oCless->tihs('key', 'taht');    //<-- triggers the error: Notice: Undefined variable
    $oClass->tihs('key', 'taht');
    echo $oClass->arr['key'];

    class MyClass {
        public $arr = array('key' => 'foo');

        function tihs($key, $value) {
            $tihs->arr[$key] = $value;  //<-- this does not cause an error message.
        }
    }
?>

undefined values in PHP are not an error. they just produce a warning if you've got the right level of display_errors/error_reporting enabled. — Marc B, Sep 05 '12 at 04:07
Make sure your error reporting includes notices, and set up a custom error handler that aborts all processing after any error is reported, whether it is a notice, warning or a real error. Then prepare to fix a lot of code which will suddenly start throwing notices. — DCoder, Sep 05 '12 at 04:08

score 1 · Answer 1 · answered Sep 05 '12 at 04:06

It is because of PHP trickery...

Under the covers, PHP is actually creating an object called tihs, adding an array to the object called arr and setting key to value.

Here is a print_r($tihs); after the assignment:

stdClass Object
(
    [arr] => Array
        (
            [key] => taht
        )

)

score 1 · Accepted Answer · edited May 23 '17 at 11:49

Normally if the error reporting level is set to E_ALL | E_STRICT (or E_ALL as of PHP 5.4.0) it should spit out an E_STRICT error. For instance, this code:

error_reporting(E_ALL | E_STRICT);
$tihs->adrr = 453;

Produces:

Strict Standards: Creating default object from empty value in [...]

Interestingly enough, if you specifically create an array instead of an ordinary variable as a property of an object that doesn't exist, e.g.:

error_reporting(E_ALL | E_STRICT);
$tihs->adrr[25] = 453;

No strict standards error is shown! It looks like this could potentially be something PHP folks might want to fix, because I'm not aware this is documented nor I think there's a legitimate reason for this behaviour.

For the record, in both cases regardless of the error a new stdClass is being created on the fly instead, like sberry mentions in his answer.

I hope it will be fixed in the future. Thanks all. – Teno Sep 05 '12 at 12:45 — Teno, Sep 05 '12 at 12:45

score 0 · Answer 3 · answered Sep 05 '12 at 04:01

0

You seemed to have misspelt $oClass as $oCless

answered Sep 05 '12 at 04:01

daveh

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score 0 · Answer 4 · answered Sep 05 '12 at 04:08

Agreed, $oCless instead of $oClass would give you an undefined variable error.

Also, "this" is a keyword in most languages and may be in php as well. You should refrain from using it so that it doesn't come out in other languages as a habit. You'll get way more errors if you're using "this" as function and variable names. You wouldn't even get things to compile.

No Error for Undefined Variable Used in Class Methods in PHP

4 Answers4