//生成唯一用户标识id
function create_guid() {
    $charid = strtoupper(md5(uniqid(mt_rand(), true)));
    $hyphen = chr(45);// "-"
    $uuid = chr(123)// "{"
        .substr($charid, 0, 8).$hyphen
        .substr($charid, 8, 4).$hyphen
        .substr($charid,12, 4).$hyphen
        .substr($charid,16, 4).$hyphen
        .substr($charid,20,12)
        .chr(125);// "}"
    return $uuid;
}