PHP中实现中文字串截取无乱码的解决方法

<?php
echo mb_substr('这样一来我的字符串就不会有乱码^_^', 0, 7, 'utf-8');
?>
输出：这样一来我的字
<?php
echo mb_strcut('这样一来我的字符串就不会有乱码^_^', 0, 7, 'utf-8');
?>

function GBsubstr($string, $start, $length) {
if(strlen($string)>$length){
  $str=null;
  $len=$start+$length;
  for($i=$start;$i<$len;$i++){
  if(ord(substr($string,$i,1))>0xa0){
   $str.=substr($string,$i,2);
   $i++;
  }else{
   $str.=substr($string,$i,1);
  }
  }
  return $str.'...';
}else{
  return $string;
}
}

function substr_text($str, $start=0, $length, $charset="utf-8", $suffix="")
{
if(function_exists("mb_substr")){
return mb_substr($str, $start, $length, $charset).$suffix;
}
elseif(function_exists('iconv_substr')){
return iconv_substr($str,$start,$length,$charset).$suffix;
}
$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));
return $slice.$suffix;
}