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

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  • Last Updated : 16 Nov, 2021

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:

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:

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(): 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:

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

Differences: The following differences exist between the two mentioned methods: 

array_keys array_key_exists
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. 


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