UUID格式:8-4-4-4-12 - 为什么？

Question

为什么UUID的格式为"8-4-4-4-12"(数字)？我已经看了看原因,但找不到要求它的决定.

格式为十六进制字符串的UUID示例:58D5E212-165B-4CA0-909B-C86B9CEE0111

Answer 1

time, version, clock_seq_hi, clock_seq_lo, node正如后续的rfc所示,它被分开.

来自IETF RFC4122:

4.1.2.  Layout and Byte Order

   To minimize confusion about bit assignments within octets, the UUID
   record definition is defined only in terms of fields that are
   integral numbers of octets.  The fields are presented with the most
   significant one first.

   Field                  Data Type     Octet  Note
                                        #

   time_low               unsigned 32   0-3    The low field of the
                          bit integer          timestamp

   time_mid               unsigned 16   4-5    The middle field of the
                          bit integer          timestamp

   time_hi_and_version    unsigned 16   6-7    The high field of the
                          bit integer          timestamp multiplexed
                                               with the version number  

   clock_seq_hi_and_rese  unsigned 8    8      The high field of the
   rved                   bit integer          clock sequence
                                               multiplexed with the
                                               variant

   clock_seq_low          unsigned 8    9      The low field of the
                          bit integer          clock sequence

   node                   unsigned 48   10-15  The spatially unique
                          bit integer          node identifier

   In the absence of explicit application or presentation protocol
   specification to the contrary, a UUID is encoded as a 128-bit object,
   as follows:

   The fields are encoded as 16 octets, with the sizes and order of the
   fields defined above, and with each field encoded with the Most
   Significant Byte first (known as network byte order).  Note that the
   field names, particularly for multiplexed fields, follow historical
   practice.

   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          time_low                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       time_mid                |         time_hi_and_version   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |clk_seq_hi_res |  clk_seq_low  |         node (0-1)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         node (2-5)                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Answer 2

格式在IETF RFC4122的第3节中定义.输出格式定义为"UUID = ..."

3.-命名空间注册模板

命名空间ID:UUID注册信息:注册日期:2003-10-01

宣布名称空间的注册人:JTC 1/SC6(ASN.1报告人组)

语法结构声明:UUID是一个空间和时间相对于所有UUID空间唯一的标识符.由于UUID是固定大小并包含时间字段,因此值可能会翻转(大约AD 3400,具体取决于所使用的特定算法).UUID可用于多种用途,从标记具有极短寿命的对象到可靠地识别网络中的非常持久的对象.

  The internal representation of a UUID is a specific sequence of
  bits in memory, as described in Section 4.  To accurately
  represent a UUID as a URN, it is necessary to convert the bit
  sequence to a string representation.

  Each field is treated as an integer and has its value printed as a
  zero-filled hexadecimal digit string with the most significant
  digit first.  The hexadecimal values "a" through "f" are output as
  lower case characters and are case insensitive on input.

  The formal definition of the UUID string representation is
  provided by the following ABNF [7]:

  UUID                   = time-low "-" time-mid "-"
                           time-high-and-version "-"
                           clock-seq-and-reserved
                           clock-seq-low "-" node
  time-low               = 4hexOctet
  time-mid               = 2hexOctet
  time-high-and-version  = 2hexOctet
  clock-seq-and-reserved = hexOctet
  clock-seq-low          = hexOctet
  node                   = 6hexOctet
  hexOctet               = hexDigit hexDigit
  hexDigit =
        "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9" /
        "a" / "b" / "c" / "d" / "e" / "f" /
        "A" / "B" / "C" / "D" / "E" / "F"

Answer 3

128 位

“8-4-4-4-12”格式仅供人类阅读。该UUID是一个真正的128位数字。

考虑字符串格式在存储或在内存中时需要字节数的两倍而不是 128 位数字。我建议在内部使用该数字，当它需要显示在 UI 上或导出到文件中时，请使用字符串格式。