array_key_first()

(PHP 7 >= 7.3.0)

Gets the first key of an array

说明

array_key_first(array $array): mixed

Get the first key of the given$arraywithout affecting the internal array pointer.

参数

$array

An array.

返回值

Returns the first key of$arrayif the array is not empty;NULLotherwise.

范例

Basicarray_key_first()Usage

<?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"

注释

There are several ways to provide this functionality for versions prior to PHP 7.3.0. It is possible to usearray_keys(), but that may be rather inefficient. It is also possible to usereset()andkey(), 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;
    }
}
?>

参见

• array_key_last()Gets the last key of an array
• reset() 将数组的内部指针指向第一个单元