Undefined array key
Description
This notice is emitted when an offset (string or integer) is being used before being defined. In a word, the element at this offset does not exist, so PHP creates it on the fly, as NULL, then uses it.
Example
<?php
// undefined array key 4
echo [1,2,3][4];
// undefined array key 'a'
echo [1,2,3]['a'];
// undefined array key 1
list($a, $b) = ['c'];
?>
Alternatives
- Test the existence of the offset before usage.
- Gives the offset a default value before usage.
- Check that the right operand of a list() call has enough elements to fit the left operand.
Related error messages
In previous PHP versions, this error message used to be :ref:undefined-offset.