php截取字符串，避免乱码

<?php
//截取中文字符串  
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;  
}  
?>  

  
<?php  
//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);  
}  
?>  

<?php  
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');  
?>  

<?php  
  
function sysSubStr($String,$Length,$Append = false)  
{  
if (strlen($String) <= $Length )  
{  
return $String;  
}  
else  
{  
$I = 0;  
while ($I < $Length)  
{  
$StringTMP = substr($String,$I,1);  
if ( ord($StringTMP) >=224 )  
{  
$StringTMP = substr($String,$I,3);  
$I = $I + 3;  
}  
elseif( ord($StringTMP) >=192 )  
{  
$StringTMP = substr($String,$I,2);  
$I = $I + 2;  
}  
else  
{  
$I = $I + 1;  
}  
$StringLast[] = $StringTMP;  
}  
$StringLast = implode("",$StringLast);  
if($Append)  
{  
$StringLast .= "...";  
}  
return $StringLast;  
}  
}  
  
$String = "CodeBit.cn -- 简单、精彩、通用";  
$Length = "18";  
$Append = false;  
echo sysSubStr($String,$Length,$Append);  
?>