How to Check if Key Exists in Array in PHP

1. Check if Key Exists in PHP Array Using the array_key_exists() Function
2. Check if Key Exists in PHP Array Using the isset() Function
3. array_key_exists() vs isset() in PHP

An array is a single variable in PHP which holds many elements inside it. Each element stored inside the array has a unique index like the primary key in DB assigned to it. You can access the element of an array using that index. Your script may need the check if a particular key exists or not to perform an operation on value. In this tutorial article, we will discuss how to check if a specific key exists or not in your array.

PHP supports three types of arrays:

1. Indexed arrays - Arrays with a numeric index, where only values are provided. Eg. array(1,2,3).
2. Associative arrays - Arrays with named keys, where the key is also defined along with value like a JSON object. Eg. array("first" => 1, "second" => 2).
3. Multidimensional arrays - Arrays containing one or more nested arrays. Eg. array(array("a", "b", "c"), array("d", "e", "f"), array("g", "h", "i")).

PHP provides two ways to find out the array contains a key or not. First, we will understand those two methods and then compare them to get our result.

Check if Key Exists in PHP Array Using the array_key_exists() Function

PHP provides in-built function array_key_exists, which checks if the given key or index exists in the provided array. array_key_exists() function works with indexed arrays and associative arrays, but nested keys in multidimensional arrays won’t be found. array_key_exists() will look for the keys within the first dimension only. If no key-value pair exits, then the array considers the numeric keys as default keys starting from zero.

Syntax of array_key_exists()

array_key_exists(string|int $key, array $array): bool

Parameters

• $key (mandatory): This parameter refers to the key/index needed to be searched for in an input array.
• $array (mandatory): This parameter refers to the original array in which we want to search the given key/index $key.

Return Values

It returns true if key/index is found or false if key/index is not found.

Example Code

<?php
  $search_array = array('first' => 1, 'second' => 2);
  if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is found in the array";
  } else {
    echo "Key does not exist";
  }
?>

Output:

The 'first' element is found in the array

Check if Key Exists in PHP Array Using the isset() Function

PHP provides function isset(), which determines if a variable is set; this means if a variable is declared and assigned value other than null. isset() will return false when a variable has been assigned to null.

Syntax of isset()

isset(mixed $var, mixed ...$vars): bool

You can pass many parameters, if many parameters are supplied, then isset() will return true only if all the passed parameters are all set. PHP evaluates from left to right and stops as soon as an unset variable is encountered.

Parameters

• $var: The first variable to be checked.
• $vars: Further variables to be checked.

Return Values

It returns true if the variable exists and has any value aside from null, otherwise false.

Example Code

<?php
  $search_array = array('first' => 1, 'second' => 2);
  if (isset($search_array['first'])) {
    echo "The 'first' element is found in the array";
  } else {
    echo "Key does not exist";
  }
?>

Output:

The 'first' element is found in the array

array_key_exists() vs isset() in PHP

isset() does not return true for array keys that correspond to a null value, while array_key_exists() does return true.

<?php
    $search_array = array('first' => null, 'second' => 2);
    echo isset($search_array['first']) ? "true" : "false";
    echo "\n";
    echo array_key_exists('first', $search_array) ? "true" : "false";
?>

Output:

false
true