php截取中英文字符函数

截取中英文字符函数
public 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);
}