PHP Australia Conference 2015

key

(PHP 4, PHP 5)

keyFetch a key from an array

Description

mixed key ( array &$array )

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.

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

The above example will output:

fruit1<br />
fruit4<br />
fruit5<br />

See Also

  • current() - Return the current element in an array
  • next() - Advance the internal array pointer of an array

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User Contributed Notes 6 notes

up
17
vinob44 at gmail dot com
11 months 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($array);
}
//this will work properly
?>
up
9
lhardie
5 months ago
Note that using key($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
11
FatBat
2 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
-6
yarco dot w at gmail dot com
7 years ago
Re: br_joris[at]hotmail[doth]com

Do you really mean you want 2 keys point to 1 value?
What you've written seems you want 1 key point to 2 values.

But if you really want 2 keys point to 1 value, you could do the following:

<?php
$buf
['key1'] = 'abc';
$buf['key2'] = & $buf['key1'];
?>
up
-13
goker.cebeci
2 years ago
object usage:

<?php

$object
= new stdClass();
$object->child->key = 'value';

echo
key((array) $object->child);
// key

?>
up
-14
michael
5 years ago
Here is an improved version of the KeyName function below. It is simpler and faster, especially on large arrays as it runs in O(1) instead of O(n).

<?php
function KeyName(array $a, $pos) {
   
$temp = array_slice($a, $pos, 1, true);
    return
key($temp);
}
?>

Also, KeyName($a, -1) will return the last key, etc.
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