隐藏中间字符

function text_hide($string, $start = 3, $length = -3, $re = '*')
{
    if (empty($string)) return false;
    $strarr = [];
    $mb_strlen = mb_strlen($string);
    while ($mb_strlen) {//循环把字符串变为数组
        $strarr[] = mb_substr($string, 0, 1, 'utf8');
        $string = mb_substr($string, 1, $mb_strlen, 'utf8');
        $mb_strlen = mb_strlen($string);
    }
    $strlen = count($strarr);
    $begin = $start >= 0 ? $start : ($strlen - abs($start));
    $end = $last = $strlen - 1;
    if ($length > 0) {
        $end = $begin + $length - 1;
    } elseif ($length < 0) {
        $end -= abs($length);
    }
    for ($i = $begin; $i <= $end; $i++) {
        $strarr[$i] = $re;
    }
    if ($begin >= $end || $begin >= $last || $end > $last) return false;
    
    return implode('', $strarr);
}