<?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 = "简明现代魔法 —— 专注于互联网主流的各种技术";
$length = "27";
$append = true;
echo sysSubStr($string,$length,$append);
// 输出
// 简明现代魔法 —— 专...
?>

<?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
/*
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');
?>