php转换unicode编码

<?php
$str = "Hello, 世界!";
$utf8_to_unicode = function($str) {
    $unicode = '';
    $len = mb_strlen($str, 'UTF-8');
    for ($i = 0; $i < $len; $i++) {
        $char = mb_substr($str, $i, 1, 'UTF-8');
        $unicode .= sprintf('U+%04X ', mb_ord($char, 'UTF-8'));
    }
    return $unicode;
};

echo $utf8_to_unicode($str);
?>

<?php
$str = "Hello, 世界!";
$utf8_to_unicode = function($str) {
    $unicode = '';
    $len = mb_strlen($str, 'UTF-8');
    for ($i = 0; $i < $len; $i++) {
        $char = mb_substr($str, $i, 1, 'UTF-8');
        if ($code = mb_ord($char, 'UTF-8')) {
            $unicode .= sprintf('U+%04X ', $code);
        } else {
            $unicode .= 'U+FFFD '; // 替换为替换字符
        }
    }
    return $unicode;
};

echo $utf8_to_unicode($str);
?>