php 为什么时间戳限制为 2038？
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Why do timestamps have a limit to 2038?
提问by Shoe
I just found out, running a calendar script, that timestamps in PHP has a limit to 2038. What does it really mean? Why is it 2038 instead of 2050 or 2039? Why a limit if timestamps just count seconds from a given date (1970)?
我刚刚在运行日历脚本时发现，PHP 中的时间戳限制为 2038。这到底是什么意思？为什么是 2038 年而不是 2050 年或 2039 年？如果时间戳只是从给定日期（1970）计算秒数，为什么要限制？
采纳答案by Matthew Scharley
The limit is imposed by the 4 byte signed integers that most C libraries use for representing that count. Quick math (assumes 365 day years, not exactly correct):
该限制是由大多数 C 库用于表示该计数的 4 字节有符号整数强加的。快速数学（假设 365 天年，不完全正确）：
2147483648 seconds ~ 68.1 years
This also implies a lower limit of ~1900. Some libraries have started to introduce 64 bit epoch counts, but they are few and far between for the moment.
这也意味着 ~1900 的下限。一些库已经开始引入 64 位纪元计数，但目前它们很少。
回答by Sander Marechal
The maximum value of a 32-bit integer is 2,147,483,647. If you add +1 to that, you get -2,147,483,647. 2,147,483,647 seconds from 01-01-1970 00:00:00 is January 19, 2038. If you add one more second, you get a date somewhere in 1902.
32 位整数的最大值为 2,147,483,647。如果你加上 +1，你会得到 -2,147,483,647。从 01-01-1970 00:00:00 开始的 2,147,483,647 秒是 2038 年 1 月 19 日。如果再增加一秒，您会得到 1902 年的某个日期。
回答by DhruvPathak
due to the limit of INT datatype on 32 bit machine
由于 32 位机器上 INT 数据类型的限制
http://php.net/manual/en/function.mktime.php
http://php.net/manual/en/function.mktime.php
From php.net : "The maximum possible date accepted by mktime() and gmmktime() is dependent on the current location time zone.
来自 php.net ：“ mktime() 和 gmmktime() 接受的最大可能日期取决于当前位置时区。
For example, the 32-bit timestamp overflow occurs at 2038-01-19T03:14:08+0000Z. But if you're in a UTC -0500 time zone (such as EST in North America), the maximum accepted time before overflow (for older PHP versions on Windows) is 2038-01-18T22:14:07-0500Z, regardless of whether you're passing it to mktime() or gmmktime()."
例如，32 位时间戳溢出发生在 2038-01-19T03:14:08+0000Z。但是，如果您处于 UTC -0500 时区（例如北美的 EST），则溢出前的最大接受时间（对于 Windows 上的旧 PHP 版本）为 2038-01-18T22:14:07-0500Z，无论无论您是将它传递给 mktime() 还是 gmmktime()。”
回答by pocketfullofcheese
my guess is that it is stored in a fixed number of bits, which means a limit on how big the timestamp can get. We could do some math to figure it out exactly.
我的猜测是它存储在固定数量的位中，这意味着时间戳可以得到多大的限制。我们可以做一些数学计算来准确地计算出来。
