array_key_first

PHP-Array

array_key_first — Gets the first key of an array

说明

array_key_first ( array $array ) : mixed

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

参数

• array
  An array.

返回值

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

范例

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];
$firstKey = array_key_first($array);
var_dump($firstKey);
?>
以上例程会输出：
string(1) "a"

Tip
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;
    }
}
?>