php字符串截取的代码学习

<?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);
?>