完整中文字符串截取長度函數

支持各種編碼

/**

* string $source 需要轉換的字符串
* string $start 開始位置
* string $length 截取長度
* string $charset 編碼格式
* string $suffix 截斷顯示字符後綴
+----------------------------------------------------------
* @return string
+----------------------------------------------------------
*/
function xs_substr($source, $start=0, $length, $charset="utf-8", $suffix="")
{
if(function_exists("mb_substr")) //采用PHP自帶的mb_substr截取字符串
{
$string = mb_substr($source, $start, $length, $charset).$suffix;
}
elseif(function_exists('iconv_substr')) //采用PHP自帶的iconv_substr截取字符串
{
$string = iconv_substr($source,$start,$length,$charset).$suffix;
}
else
{
$pattern['utf-8'] = "/[x01-x7f]|[xc2-xdf][x80-xbf]|[xe0-xef][x80-xbf]{2}|[xf0-xff][x80-xbf]{3}/";
$pattern['gb2312'] = "/[x01-x7f]|[xb0-xf7][xa0-xfe]/";
$pattern['gbk'] = "/[x01-x7f]|[x81-xfe][x40-xfe]/";
$pattern['big5'] = "/[x01-x7f]|[x81-xfe]([x40-x7e]|xa1-xfe])/";
preg_match_all($pattern[$charset], $source, $match);
$slice = join("",array_slice($match[0], $start, $length));

$string = $slice.$suffix;
}
return $string;
}