PHP截取中文字符串函数~包括GB2312和UT-8

/*
Utf-8、gb2312都支持的汉字截取函数
cut_str(字符串, 截取长度, 开始长度, 编码);
编码默认为 utf-8
开始长度默认为 0
*/

function cut_str($string, $sublen, $start = 0, $code = 'UTF-8')
{
if($code == 'UTF-8')
{
$pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
preg_match_all($pa, $string, $t_string);

if(count($t_string[0]) - $start > $sublen) return join('', array_slice($t_string[0], $start, $sublen))."...";  
        return join('', array_slice($t_string[0], $start, $sublen));  
    }  
    else  
    {  
        $start = $start*2;  
        $sublen = $sublen*2;  
        $strlen = strlen($string);  
        $tmpstr = '';  
  
        for($i=0; $i< $strlen; $i++)
{
if($i>=$start && $i< ($start+$sublen))
{
if(ord(substr($string, $i, 1))>129)  
                {  
                    $tmpstr.= substr($string, $i, 2);  
                }  
                else  
                {  
                    $tmpstr.= substr($string, $i, 1);  
                }  
            }  
            if(ord(substr($string, $i, 1))>129) $i++;  
        }  
        if(strlen($tmpstr)< $strlen ) $tmpstr.= "...";
return $tmpstr;
}
}

$str = "abcd需要截取的字符串";
echo cut_str($str, 8, 0, 'gb2312');
?>  


//截取中文字符串
//支持GB2312
function mysubstr($str, $start, $len) {
$tmpstr = "";
$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;  
    }  
?>  



//截取utf8字符串
function utf8Substr($str, $from, $len)
{
return preg_replace('#^(?:[\x00-\x7F]|[\xC0-\xFF][\x80-\xBF]+){0,'.$from.'}'.
'((?:[\x00-\x7F]|[\xC0-\xFF][\x80-\xBF]+){0,'.$len.'}).*#s',
'$1',$str);
}
?>