Mastering PHP’s array_key_exists: Check If a Key Exists in an Array

The PHP function array_key_exists() returns TRUE when a specified key or index is present in an array (or object) and FALSE otherwise. The key can be any value that is valid as an array index.

Function Signature

bool array_key_exists(mixed $key, array $search)

Parameters

$key : The key to check for.

$search : The array (or object) in which to look for the key.

Return Value

Returns TRUE on success (key exists) and FALSE on failure.

Example 1 – Basic Array Check

<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

This script creates an associative array and uses array_key_exists() to test whether the key 'first' is present, printing a message when it is.

Example 2 – Comparing with isset()

<?php
$search_array = array('first' => null, 'second' => 4);
// array_key_exists returns true because the key exists even though its value is null
var_dump(array_key_exists('first', $search_array)); // bool(true)
// isset returns false because the value is null
var_dump(isset($search_array['first'])); // bool(false)
?>

This example demonstrates that array_key_exists() checks for the existence of the key regardless of its value, whereas isset() returns false for keys with null values.