array_key_first
(PHP 7 >= 7.3.0)
array_key_first — Gets the first key of an array
说明
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
Example #1 Basic array_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
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;
}
}
?>
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