php隐藏字符串中间部分字符

    经常在公布中奖名单时，为了避免曝光中奖者的手机号码，于是采用隐藏中间部分数字来呈现，比如：139****2972，本文简单分享一段php实现的代码，大神可以忽略，菜鸟继续。

// 隐藏部分字符串
function func_substr_replace($str, $replacement = "*", $start = 1, $length = 3)
{
    $len = mb_strlen($str,"utf-8");
    if ($len > intval($start+$length)) {
        $str1 = mb_substr($str,0,$start,"utf-8");
        $str2 = mb_substr($str,intval($start+$length),NULL,"utf-8");
    } else {
        $str1 = mb_substr($str,0,1,"utf-8");
        $str2 = mb_substr($str,$len-1,1,"utf-8");    
        $length = $len - 2;        
    }
    $new_str = $str1;
    for ($i = 0; $i < $length; $i++) { 
        $new_str .= $replacement;
    }
    $new_str .= $str2;

    return $new_str;
}