key

(PHP 4, PHP 5, PHP 7, PHP 8)

keyFetch a key from an array

Description

key(array|object $array): int|string|null

key() returns the index element of the current array position.

Parameters

array

The array.

Return Values

The key() function simply returns the key of the array element that's currently being pointed to by the internal pointer. It does not move the pointer in any way. If the internal pointer points beyond the end of the elements list or the array is empty, key() returns null.

Changelog

Version Description
8.1.0 Calling this function on objects is deprecated. Either convert the object to an array using get_mangled_object_vars() first, or use the methods provided by a class that implements Iterator, such as ArrayIterator, instead.
7.4.0 Instances of SPL classes are now treated like empty objects that have no properties instead of calling the Iterator method with the same name as this function.

Examples

Example #1 key() example

<?php
$array
= array(
'fruit1' => 'apple',
'fruit2' => 'orange',
'fruit3' => 'grape',
'fruit4' => 'apple',
'fruit5' => 'apple');

// this cycle echoes all associative array
// key where value equals "apple"
while ($fruit_name = current($array)) {
if (
$fruit_name == 'apple') {
echo
key($array), "\n";
}
next($array);
}
?>

The above example will output:

fruit1
fruit4
fruit5

See Also

add a note

User Contributed Notes 5 notes

up
414
lhardie
10 years ago
Note that using key($array) in a foreach loop may have unexpected results.

When requiring the key inside a foreach loop, you should use:
foreach($array as $key => $value)

I was incorrectly using:
<?php
foreach($array as $value)
{
$mykey = key($array);
}
?>

and experiencing errors (the pointer of the array is already moved to the next item, so instead of getting the key for $value, you will get the key to the next value in the array)

CORRECT:
<?php
foreach($array as $key => $value)
{
$mykey = $key;
}

A noob error, but felt it might help someone else out there.
up
54
vinob44 at gmail dot com
10 years ago
Suppose if the array values are in numbers and numbers contains `0` then the loop will be terminated. To overcome this you can user like this

<?php
$array
= array(
'0' => '5',
'1' => '2',
'2' => '0',
'3' => '3',
'4' => '1');

// wrong approach

while ($fruit_name = current($array)) {

echo
key($array).'<br />';
next($array);
}

// the way will be break loop when arra('2'=>0) because its value is '0', while(0) will terminate the loop

// correct approach
while ( ($fruit_name = current($array)) !== FALSE ) {

echo
key($array).'<br />';
next($array);
}
//this will work properly
?>
up
21
FatBat
12 years ago
Needed to get the index of the max/highest value in an assoc array.
max() only returned the value, no index, so I did this instead.

<?php
reset
($x); // optional.
arsort($x);
$key_of_max = key($x); // returns the index.
?>
up
-11
Md Tahazzot
4 years ago
(Editor note: Or just use the array_keys function)

Make as simple as possible but not simpler like this one :)

$k = array();
for($i = 0; $i < count($arr); $i++){
$k[$i] = key($arr);
next($arr);
}
up
-18
danielmadsv at gmail dot com
5 years ago
In addition to FatBat's response, if you'd like to find out the highest key in an array (assoc or not) but don't want to arsort() it, take a look at this:

<?php

$arr
= [ '3' => 14, '1' => 15, '4' => 92, '15' => 65 ];

$key_of_max = array_search( max($arr) , $arr);

?>
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