<?php 
 
/**
 +----------------------------------------------------------
 * 將一個字符串部分字符用*替代隱藏
 +----------------------------------------------------------
 * @param string $string 待轉換的字符串
 * @param int  $bengin 起始位置，從0開始計數，當$type=4時，表示左側保留長度
 * @param int  $len  需要轉換成*的字符個數，當$type=4時，表示右側保留長度
 * @param int  $type  轉換類型：0，從左向右隱藏；1，從右向左隱藏；2，從指定字符位置分割前由右向左隱藏；3，從指定字符位置分割后由左向右隱藏；4，保留首末指定字符串
 * @param string $glue  分割符
 +----------------------------------------------------------
 * @return string 處理后的字符串
 +----------------------------------------------------------
 */
function hideStr($string, $bengin = 0, $len = 4, $type = 0, $glue = "@") {
	if (empty($string))
		return false;
	$array = array();
	if ($type == 0 || $type == 1 || $type == 4) {
		$strlen = $length = mb_strlen($string);
		while ($strlen) {
			$array[] = mb_substr($string, 0, 1, "utf8");
			$string = mb_substr($string, 1, $strlen, "utf8");
			$strlen = mb_strlen($string);
		}
	}
	if ($type == 0) {
		for ($i = $bengin; $i < ($bengin + $len); $i++) {
			if (isset($array[$i]))
				$array[$i] = "*";
		}
		$string = implode("", $array);
	} else if ($type == 1) {
		$array = array_reverse($array);
		for ($i = $bengin; $i < ($bengin + $len); $i++) {
			if (isset($array[$i]))
				$array[$i] = "*";
		}
		$string = implode("", array_reverse($array));
	} else if ($type == 2) {
		$array = explode($glue, $string);
		$array[0] = hideStr($array[0], $bengin, $len, 1);
		$string = implode($glue, $array);
	} else if ($type == 3) {
		$array = explode($glue, $string);
		$array[1] = hideStr($array[1], $bengin, $len, 0);
		$string = implode($glue, $array);
	} else if ($type == 4) {
		$left = $bengin;
		$right = $len;
		$tem = array();
		for ($i = 0; $i < ($length - $right); $i++) {
			if (isset($array[$i]))
				$tem[] = $i >= $left ? "*" : $array[$i];
		}
		$array = array_chunk(array_reverse($array), $right);
		$array = array_reverse($array[0]);
		for ($i = 0; $i < $right; $i++) {
			$tem[] = $array[$i];
		}
		$string = implode("", $tem);
	}
	return $string;
}
 
 
$str = '12345678901';
echo hideStr($str,2,4);