C++ 如何将时间uuid（存储在boost uuid中）转换为时间戳/自历元起的时间？

从UUID时间戳到EPOCH以来的秒数的转换似乎非常容易，也基于

然而，当我尝试这样做时，我总是得到错误的值。我做错了什么，我不知道是什么

为此，我使用了和提供的示例UUID值

我们所要做的就是从UUID原始数据中获取第一个

uint64\t

，屏蔽其前四个MSb，减去一个差，然后除以一个数字

以下是我的最低完整示例：

#include <boost/date_time.hpp>
#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_generators.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <cstdint>
#include <iostream>

uint64_t TimestampFromUUID(const boost::uuids::uuid& uuid) {
  static constexpr const int UUID_SIZE = 16;
  static_assert(sizeof(uuid) == UUID_SIZE, "Invalid size of uuid");

  static constexpr const int MS_FROM_100NS_FACTOR = 10000;
  static constexpr const uint64_t OFFSET_FROM_15_10_1582_TO_EPOCH = 122192928000000000;

  struct two64s {
    uint64_t n1;
    uint64_t n2;
  } contents;
  std::memcpy(&contents, uuid.data, UUID_SIZE);
  //    contents.n1 = __builtin_bswap64(contents.n1);
  uint64_t timestamp = contents.n1 & UINT64_C(0x0FFFFFFFFFFFFFFF);
  return (timestamp - OFFSET_FROM_15_10_1582_TO_EPOCH) / MS_FROM_100NS_FACTOR;
}

int main() {
  std::cout << "Time now: " << (boost::posix_time::second_clock::universal_time() - boost::posix_time::ptime(boost::gregorian::date(1970, 1, 1))).total_milliseconds() << std::endl;
  auto gen = boost::uuids::string_generator();
  std::cout << "UUID: " << gen("49cbda60-961b-11e8-9854-134d5b3f9cf8") << std::endl;
  std::cout << "Time from UUID: " << TimestampFromUUID(gen("49cbda60-961b-11e8-9854-134d5b3f9cf8")) << std::endl;
  std::cout << "UUID: " << gen("58e0a7d7-eebc-11d8-9669-0800200c9a66") << std::endl;
  std::cout << "Time from UUID: " << TimestampFromUUID(gen("58e0a7d7-eebc-11d8-9669-0800200c9a66")) << std::endl;

  return 0;
}

您可以使用此源代码

---

为什么我的结果甚至不接近当前的时间戳？我做错了什么？

我知道你一直做得不好。在阅读您提供的文档时，我尝试从UUID重新生成时间戳。下面是我的代码：

uint64_t TimestampFromUUID(const boost::uuids::uuid& uuid) {
  static constexpr const int UUID_SIZE = 16;
  static_assert(sizeof(uuid) == UUID_SIZE, "Invalid size of uuid");

  static constexpr const int MS_FROM_100NS_FACTOR = 10000;
  static constexpr const uint64_t OFFSET_FROM_15_10_1582_TO_EPOCH = 122192928000000000;

  uint64_t timestamp = uuid.data[3] + (uuid.data[2] << 8) + (uuid.data[1] << 16) + (uuid.data[0] << 24);
  timestamp += ((uint64_t)uuid.data[4] << 40) + ((uint64_t)uuid.data[5] << 32);
  timestamp += ((uint64_t)uuid.data[7] << 48) + ((uint64_t)(uuid.data[6] & 0x0F) << 56);
  return (timestamp - OFFSET_FROM_15_10_1582_TO_EPOCH) / MS_FROM_100NS_FACTOR;
}

uint64\u t TimestampFromUUID（常量boost:：uuid:：uuid&uuid）{
静态constexpr const int UUID_SIZE=16；
静态_断言（sizeof（uuid）=uuid_大小，“uuid的大小无效”）；
静态constexpr const int MS_FROM_100NS_因数=10000；
静态constexpr const uint64_t OFFSET_从_15_10_1582_到_EPOCH=12219292800000000；
uint64_t timestamp=uuid.data[3]+（uuid.data[2]我认为通过将uuid处理为字符串并使用字符串操作提取时间戳信息，然后将其转换为数值，会更容易理解。诀窍在于时间戳信息存储在uuid中的方式。根据规范：

UUID字符串表示的形式定义如下
由以下ABNF[7]提供：

  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"

以下是UUID的字符串表示形式的示例
作为瓮：

urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6

i、 e.UUID的第一部分（在“-”之前）是时间低，第二部分是时间中，第三部分是时间高版本，第一个字符是UUID版本。因此我们需要拆分UUID并重新组合这些时间戳部分，以创建完整的时间戳字符串，如下所示：{time high减version}{time mid}{time low}

下面是修改后的代码。我以这个漂亮的javascript示例作为参考：

谢谢你指出MSb，你是对的。我纠正了。但那个掩蔽并不是真的正确。你掩蔽了8位。虽然它更接近，但它仍然偏离了10%（从新纪元开始的几年）。@量子物理学家在我的答案中做了一个重大改变，我建议你看看；）
  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"

#include <boost/date_time.hpp>
#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_generators.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <boost/algorithm/string.hpp>
#include <string>
#include <vector>
#include <cstdint>
#include <iostream>

uint64_t TimestampFromUUID(const boost::uuids::uuid& uuid) {
  static constexpr const int UUID_SIZE = 16;
  static_assert(sizeof(uuid) == UUID_SIZE, "Invalid size of uuid");

  static constexpr const int MS_FROM_100NS_FACTOR = 10000;
  static constexpr const uint64_t OFFSET_FROM_15_10_1582_TO_EPOCH = 122192928000000000;

  /* convert uuid to string for manipulation */
  std::string uuid_str = boost::uuids::to_string(uuid);
  /* store uuid parts in a vector */
  std::vector<std::string> uuid_parts;

  /* split uuid with '-' as delimiter */
  boost::split(uuid_parts, uuid_str, [](char c){return c == '-';});

  /* first part of uuid is time-low
     second part is time-mid
     third part is time high with most significant 4 bits as uuid version
  */
  std::string uuid_timestamp = uuid_parts[2].substr(1) + uuid_parts[1] + uuid_parts[0];
  std::cout << std::endl << "UUID Timestamp : " << uuid_timestamp << std::endl;

  uint64_t timestamp = std::stoul(uuid_timestamp, nullptr, 16);

  return (timestamp - OFFSET_FROM_15_10_1582_TO_EPOCH) / MS_FROM_100NS_FACTOR;
}

int main() {
  std::cout << "Time now: " << (boost::posix_time::second_clock::universal_time() - boost::posix_time::ptime(boost::gregorian::date(1970, 1, 1))).total_milliseconds() << std::endl;
  auto gen = boost::uuids::string_generator();
  std::cout << "UUID: " << gen("49cbda60-961b-11e8-9854-134d5b3f9cf8") << std::endl;
  std::cout << "Time from UUID: " << TimestampFromUUID(gen("49cbda60-961b-11e8-9854-134d5b3f9cf8")) << std::endl;
  std::cout << "UUID: " << gen("58e0a7d7-eebc-11d8-9669-0800200c9a66") << std::endl;
  std::cout << "Time from UUID: " << TimestampFromUUID(gen("58e0a7d7-eebc-11d8-9669-0800200c9a66")) << std::endl;

  return 0;
}

Time now: 1571838175000
UUID: 49cbda60-961b-11e8-9854-134d5b3f9cf8
Time from UUID: 
UUID Timestamp : 1e8961b49cbda60
1533190458118
UUID: 58e0a7d7-eebc-11d8-9669-0800200c9a66
Time from UUID: 
UUID Timestamp : 1d8eebc58e0a7d7
1092575371981