GUID生成函数

/** * GUID生成函数 * @return string */function create_guid() {    $charid = strtoupper(md5(uniqid(mt_rand(), true)));    $hyphen = chr(45);// "-"    $uuid =      substr($charid, 0, 8).$hyphen    .substr($charid, 8, 4).$hyphen    .substr($charid,12, 4).$hyphen    .substr($charid,16, 4).$hyphen    .substr($charid,20,12);    return $uuid;}