php实现中文字串截取无乱码的方法

function msubstr($str, $start=0, $length, $charset="utf-8", $suffix=true)
    {
        if(function_exists("mb_substr"))
            return mb_substr($str, $start, $length, $charset);
        elseif(function_exists('iconv_substr')) {
            return iconv_substr($str,$start,$length,$charset);
        }
        $re['utf-8']   = "/[x01-x7f]|[xc2-xdf][x80-xbf]|[xe0-xef][x80-xbf]{2}|[xf0-xff][x80-xbf]{3}/";
        $re['gb2312'] = "/[x01-x7f]|[xb0-xf7][xa0-xfe]/";
        $re['gbk']    = "/[x01-x7f]|[x81-xfe][x40-xfe]/";
        $re['big5']   = "/[x01-x7f]|[x81-xfe]([x40-x7e]|xa1-xfe])/";
        preg_match_all($re[$charset], $str, $match);
        $slice = join("",array_slice($match[0], $start, $length));
        if($suffix) return $slice."…";
        return $slice;
    }

<?php
//$start：指定开始截取字符串的位置；$length指定截取字符的长度
function substr2($string, $start, $length)
{
$len = strlen($string);
if($len > $length)
{
   $str = '';
   $len1 = $start + $length; //截取到原字符串的位置
   for($i=$start; $i<$len1; $i++)
   {
    if(ord(substr($string, $i, 2)) > 0xa0) //在ASCII中，0xa0表示汉字的开始
    {
     $str.=substr($string, $i, 2);
     $i++;
    }
    else
    {
     $str.=substr($string, $i, 1);
    }
   }
   return $str.'...';
}
else
{
   return $string;
}
}

?>

<?php
function chinesesubstr($str, $start, $len){
   $strlen = $start + $len;
   for($i=0; $i<$strlen; $i++){
    if(ord(substr($str, $i, 1)) > 0xa0){
     $tmpstr .= substr($str, $i, 2);
     $i++;
    }else{
     $tmpstr .= substr($str, $i, 1);
    }
   }
   return $tmpstr;
}
$str = "waiting for you 等wait你back";
echo chinesesubstr($str, 0, 19)
?>