PHP 7.0.6 Released

    key

    (PHP 4, PHP 5, PHP 7)

    key — Fetch 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

    User Contributed Notes

    lhardie
    2 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.
    vinob44 at gmail dot com
    2 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
    ?>
    FatBat
    4 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.
    ?>
    art
    1 year ago
    Returns "Warning" message if given parameter is not an array.
    yarco dot w at gmail dot com
    8 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'];
    ?>
    goker.cebeci
    4 years ago
    object usage:

    <?php

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

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

    ?>
    Anonymous
    1 year ago
    <?php
    function generarCodigo($longitud) {
    $key = '';
    $pattern = '123456789ASKKDOQEMANDOASJDSO';
    $max = strlen($pattern)-1;
    for(    $i=0;$i < $longitud;$i++) $key .= $pattern{mt_rand(0,$max)};
    return     $key;
    }
     


    echo     generarCodigo(4)
    echo     "-";
    echo     generarCodigo(4);
    echo     "-";
    echo     generarCodigo(4);
    echo     "-";
    echo     generarCodigo(4);
    ?>
    michael
    7 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.
    To Top