Undefined variable $%S

Description

This error appears when a variable is used, aka read, while it was not defined before.

This might be a variable passed by argument to a method; a variable used with a short assignation operator or an argument of the PHP native function compact.

Example

<?php

$x += 1;

foo($a);

compact('undefined');

function foo($a) {}

?>

Solutions

  • Use another variable.

  • Check the variable before usage.

  • Give a default value to the variable before usage.