中文如何转换为bytes[]

$s = "广东";
$s = iconv('gbk', 'utf-8', $s);
$r = array_map('ord', str_split($s));
print_r($r);

Array
(
    [0] => 229
    [1] => 185
    [2] => 191
    [3] => 228
    [4] => 184
    [5] => 156
)

$s = "广东";
$s = iconv('gbk', 'utf-8', $s);
$r = unpack('C*', $s);
print_r($r);

Array
(
    [1] => 229
    [2] => 185
    [3] => 191
    [4] => 228
    [5] => 184
    [6] => 156
)

$s = "广东";
$s = iconv('gbk', 'utf-8', $s);
$r = unpack('c*', $s);
print_r($r);

Array
(
    [1] => -27
    [2] => -71
    [3] => -65
    [4] => -28
    [5] => -72
    [6] => -100
)