PHP生成全球唯一码

<? function guid() {$charid = strtoupper(md5(uniqid(mt_rand(), true)));$uuid =substr($charid, 0, 8).substr($charid, 8, 4). substr($charid,12, 4).substr($charid,16, 4).substr($charid,20,12); return $uuid; } echo strlen(guid());?>