如何在PHP中获取字符串的字节值？

$str = "Hello, world!";
$len = strlen($str);

for ($i = 0; $i < $len; $i++) {
    $byte = ord($str[$i]);
    echo "Byte value of character " . $i . " is: " . $byte . "\n";
}

$byteArray = unpack('C*', $str);
print_r($byteArray);

Byte value of character 0 is: 72
Byte value of character 1 is: 101
Byte value of character 2 is: 108
Byte value of character 3 is: 108
Byte value of character 4 is: 111
Byte value of character 5 is: 44
Byte value of character 6 is: 32
Byte value of character 7 is: 119
Byte value of character 8 is: 111
Byte value of character 9 is: 114
Byte value of character 10 is: 108
Byte value of character 11 is: 100
Byte value of character 12 is: 33
Array
(
    [1] => 72
    [2] => 101
    [3] => 108
    [4] => 108
    [5] => 111
    [6] => 44
    [7] => 32
    [8] => 119
    [9] => 111
    [10] => 114
    [11] => 108
    [12] => 100
    [13] => 33
)