array_key_last返回数组的最后一个键

/**
 * Gets the last key of an array
 *
 * Get the last key of the given array without affecting the internal array pointer.
 *
 * @link https://secure.php.net/array_key_last
 * @param array $array An array
 * @return string|int|null Returns the last key of array if the array is not empty; NULL otherwise.
 * @since 7.3
 */
function array_key_last(array $array) { }

示例：

$array = [
    'a' => 'cat',
    'b' => 'dog',
    'c' => 'pig'
];

$result = array_key_last($array);

var_dump($result);

//结果
//string(1) "c"