PHP array_key_last Function

last modified March 13, 2025

The PHP array_key_last function returns the last key of an array without affecting the internal array pointer. It's useful for array traversal.

Basic Definition

The array_key_last function retrieves the last key from an array. It works with both indexed and associative arrays.

Syntax: array_key_last(array $array): int|string|null. Returns null for empty arrays. Introduced in PHP 7.3.

Basic array_key_last Example

This demonstrates getting the last key from a simple indexed array.

basic_array_key_last.php

<?php

$colors = ['red', 'green', 'blue'];
$lastKey = array_key_last($colors);

echo "Last key: $lastKey";

The function returns 2, which is the index of the last element 'blue'. Indexed arrays start counting from 0.

Associative Array Example

Get the last key from an associative array with string keys.

associative_array.php

<?php

$user = [
    'name' => 'John',
    'age' => 34,
    'email' => 'john@example.com'
];

$lastKey = array_key_last($user);

echo "Last key: $lastKey";

The function returns 'email', the last key in the associative array. Order is preserved as per the array definition.

Empty Array Behavior

array_key_last returns null when called on an empty array.

empty_array.php

<?php

$emptyArray = [];
$lastKey = array_key_last($emptyArray);

var_dump($lastKey);

The function safely handles empty arrays by returning null. This helps avoid errors when processing dynamic array data.

Mixed Key Types Example

The function works with arrays containing both numeric and string keys.

mixed_keys.php

<?php

$mixedArray = [
    0 => 'zero',
    'one' => 1,
    2 => 'two',
    'three' => 3
];

$lastKey = array_key_last($mixedArray);

echo "Last key: "; 
var_dump($lastKey);

The function correctly identifies 'three' as the last key regardless of the mixed key types in the array.

Practical Usage Example

Use array_key_last to get the last item in a configuration array.

practical_usage.php

<?php

$config = [
    'debug' => true,
    'log_level' => 'warning',
    'timeout' => 30,
    'last_modified' => '2025-03-13'
];

$lastKey = array_key_last($config);
$lastValue = $config[$lastKey];

echo "Last config item: $lastKey = $lastValue";

This shows how to access both the last key and its value. Useful for getting the most recent item in ordered data.

Best Practices

Check for null: Always verify the return value isn't null.
Preserve order: Remember array order matters for this function.
Performance: Faster than array_keys() for large arrays.
Readability: More clear than end()+key() alternatives.

Source

PHP array_key_last Documentation

This tutorial covered the PHP array_key_last function with practical examples showing its usage for array key retrieval scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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