(PHP 7 >= 7.3.0)
array_key_first — Gets the first key of an array
Get the first key of the given array without affecting
the internal array pointer.
arrayAn array.
Returns the first key of array if the array is not empty;
NULL otherwise.
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"