key

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

key — Devuelve una clave de un array asociativo

Descripción

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

key() devuelve la clave actual en el array array.

Parámetros

array: El array.

Valores devueltos

La función key() devuelve simplemente la clave del elemento del array que es actualmente apuntado por el puntero interno. Esta función no modifica en ningún caso la posición de este puntero. Si el puntero interno apunta un elemento situado después del final de la lista de elementos, o bien si el array está vacío, la función key() devolverá null.

Historial de cambios

Versión	Descripción
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.

Ejemplos

Ejemplo #1 Ejemplo con key()

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

// Este ciclo muestra todas las claves
// cuyo valor es "apple"
while ($fruit_name = current($array)) {
    if ($fruit_name == 'apple') {
        echo key($array), "\n";
    }
    next($array);
}
?>

El resultado del ejemplo sería:

fruit1
fruit4
fruit5

Ver también

current() - Devuelve el elemento actual del array
next() - Avance el puntero interno de un array
array_key_first() - Recupera la primera clave de un array
foreach

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User Contributed Notes 3 notes

down

414

lhardie ¶

11 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.

down

vinob44 at gmail dot com ¶

11 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
?>

down

FatBat ¶

13 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.
?>

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