array_key_first

(PHP 7 >= 7.3.0)

array_key_first — Gets the first key of an array

説明

array_key_first ( array $array ) : mixed

Get the first key of the given array without affecting the internal array pointer.

パラメータ

array

An array.

返り値

Returns the first key of array if the array is not empty; NULL otherwise.

例

例1 Basic array_key_first() Usage

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];

$firstKey = array_key_first($array);

var_dump($firstKey);
?>

上の例の出力は以下となります。

string(1) "a"

注意

ヒント

There are several ways to provide this functionality for versions prior to PHP 7.3.0. It is possible to use array_keys(), but that may be rather inefficient. It is also possible to use reset() and key(), but that may change the internal array pointer. An efficient solution, which does not change the internal array pointer, written as polyfill:

<?php
if (!function_exists('array_key_first')) {
    function array_key_first(array $arr) {
        foreach($arr as $key => $unused) {
            return $key;
        }
        return NULL;
    }
}
?>

参考

  • array_key_last() - Gets the last key of an array
  • reset() - 配列の内部ポインタを先頭の要素にセットする