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";
}
?>

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)

check array has keys in php

<?php

// The values in this arrays contains the names of the indexes (keys) 
// that should exist in the data array
$required = array('key1', 'key2', 'key3');

$data = array(
    'key1' => 10,
    'key2' => 20,
    'key3' => 30,
    'key4' => 40,
);

if (count(array_intersect_key(array_flip($required), $data)) === count($required)) {
    // All required keys exist!
}