支持多種編碼的中文字符串截取函數

function csubstr($str, $start=0, $length, $charset="utf-8", $suffix=true)
{
if(function_exists("mb_substr"))
return mb_substr($str, $start, $length, $charset);
$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, $length));
if($suffix) return $slice."…";
return $slice;
}