带有utf-8的php substr()函数在最后留下 标记

substr(string $string, int $start, int|null $length = null): string|false

function substr_with_last_marker(string $string, int $length): string {
    $last_char = mb_substr($string, $length - 1, 1, 'utf-8');
    $substr = mb_substr($string, 0, $length - 1, 'utf-8');
    return $substr . $last_char;
}

// 示例用法
$string = "带有utf-8的php substr()函数在最后留下标记";
$length = 10;
$result = substr_with_last_marker($string, $length);
echo $result;