Fix – PHP Notice: Use of undefined constant. (Mostly used in the product_info.php/html files)
or
Error Type: [E_NOTICE] Undefined variable: extrafields etc
This is a common notice / warning that occurs whenever PHP has detected the usage of an undefined constant. In case you didn’t already know, a constant is a simple value that cannot change during the execution of a script. i.e. If you define constant A as “123”, you won’t be able to change it to “456” at a later stage.
An example of a constant being defined in PHP:
<?php
//create a constant called PI
define('PI', 3.14);
//print it out to the screen.
echo PI;
PI is a good example of a constant, simply because the value for PI never changes. It will always be 3.14 and nothing in our code should be able to change that.
In some cases, this kind of notice can appear, even though the developer isn’t using any constants.
Forgetting to use a $ symbol at the start of a variable name.
<?php
//Create a simple variable called $name.
$name = "Wayne";
//Print it out.
echo name;
n the above example, I have forgotten to place a dollar sign ($) in front of my $name variable. This will result in the error:
Notice: Use of undefined constant name – assumed ‘name’
