key

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

    key — Fetch 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

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    User Contributed Notes 3 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
    52
    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.
    ?>
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