What are the differences between array_keys() and array_key_exists() in PHP ?

The following article indicates the differences between the two inbuilt functions array_keys() and array_key_exists() in PHP.

array_keys() Function

The array_keys() function is used to return all the keys or a subset of the array keys. This function works for both indexed as well as associative arrays. 

Syntax

array_keys(array, value, strict);

Parameters 

• array: An array with keys to check.
• value: The value to retrieve the keys for.
• strict: The parameter to check the data type of the variable or not.

Example 1: This example illustrates the basic usage of the array_keys() Function in PHP.

PHP

<?php
$arr = array(
    "Java" => "SpringBoot",
    "PHP 4.0" => "CodeIgniter",
    "Python" => "Django",
    "PHP 3.0" => "CodeIgniter"
);

// Searching for keys of codeigniter
$key1 = array_keys($arr, "CodeIgniter");
print("Keys for CodeIgniter : ");
print_r($key1);
print("</br>");

// Searching for keys of wordpress
$key2 = array_keys($arr, "WordPress");
print("Keys for WordPress : ");
print_r($key2);
?>

Output:

Keys for CodeIgniter : Array ( [0] => PHP 4.0 [1] => PHP 3.0 )
Keys for WordPress : Array ( )

Example 2: This is another example that illustrates the basic usage of the array_keys() Function in PHP.

PHP

<?php
$arr = array(1, 2, 3, 4, 5);

// Searching for keys of string 5
// using strict parameter true
$key1 = array_keys($arr, "5", true);
print ("Keys for '5' : ");
print_r($key1);
echo ("</br>");

// Searching for keys of string 5
// using strict parameter false
$key2 = array_keys($arr, "5", false);
print ("Keys for '5' : ");
print_r($key2);
?>

Output:

Keys for '5' : Array ( )
Keys for '5' : Array ( [0] => 4 )

array_key_exists() Function

The array_key_exists() method in PHP is used to validate an array for a specified key. It returns a boolean value of “true” if the key exists and “false” if the key does not exist in the array.

Syntax

array_key_exists(key, array);

Parameters

• key: The values to check.
• array: An array with keys to check.

Example 1: This example illustrates the basic usage of the array_key_exists() Function in PHP.

PHP

<?php
$arr = array(1, 2, 3, 4, 5);

// Searching for keys of string 5
$key1 = array_key_exists('4', $arr);
if ($key1)
{
    echo ("Key exists");
}
else
{
    echo ("Key does not exist");
}
?>

Output:

key exists

Example 2: This example demonstrates the array_key_exists() function in PHP based on some key in the array holding key-value pairs.

PHP

<?php
$myarray = array(
    "ram" => 25,
    "krishna" => 10,
    "aakash" => 20,
    "gaurav"
);

// Searching for keys
$key1 = array_key_exists('krishna', $myarray);
if ($key1)
{
    echo ("Key exists" . " for 'krishna'");
}
else
{
    echo ("Key does not exist");
}
print_r("<br>");
$key2 = array_key_exists('balram', $myarray);
if ($key2)
{
    echo ("Key exists" . " for 'balram'");
}
else
{
    echo ("Key does not exist" . " for 'balram'");
}
?>

Output:

Key exists for 'krishna'
Key does not exist for 'balram'

Example 3: This example demonstrates the array_key_exists() function in PHP based on the $index value by the user.

PHP

<?php
$myarray = array(
    "ram",
    "krishna",
    "aakash",
    "gaurav"
);

$index1 = 1;
$key1 = array_key_exists($index1, $myarray);
if ($key1)
{
    echo ("Key exists for index " . $index1);
}
else
{
    echo ("Key does not exist for index " . $index1);
}
print_r("<br>");
$index2 = 5;
$key2 = array_key_exists($index2, $myarray);
if ($key2)
{
    echo ("Key exists for index " . $index2);
}
else
{
    echo ("Key does not exist for index " . $index2);
}
?>

Output:

Key exists for index 1
Key does not exist for index 5

Differences between the array_keys() and array_key_exists() Methods

array_keys() Methods	array_key_exists() Methods
It checks if the corresponding value is mapped to any key in the array.	It checks if a key exists in the array.
It returns an array.	It returns a boolean value.
It works for both uni and multi-dimensional arrays.	It works only for uni-dimensional arrays.
It can be used to match data type using strict parameter	It can  be used to match the only value
It can also be used to retrieve all the keys of the array if the value parameter is blank.	It simply checks for the specified key in the array.