PHP

php key in array exists

<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

php array exists key

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

array_key_exists vs in_array

in_array() v/s array_key_exists()
Difference:

in_array() checks if a value exists in an array (checks the values, not the keys) and returns true, or false otherwise.
while:

array_key_exists() checks if the given key or index exists in the array (checks in keys, not in values) and returns true, or false otherwise.
Visits the manual (links above) for examples and more information.

php array has key

array_key_exists('key', $your_array);

array_key_exists

<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

array_key_exists

array_key_exists($key_to_search, $array)