为什么时间戳限制为2038?

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我刚刚发现，运行日历脚本时，PHP中的时间戳限制为2038年.这实际上是什么意思?为什么是2038，而不是2050或2039?如果时间戳记仅是从给定日期(1970年)起算的秒数，为什么还要设置限制?

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)?

推荐答案

限制是由大多数C库用来表示该计数的4字节带符号整数强加的.快速数学(假设365天年，并非完全正确):

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):

2147483648 seconds ~ 68.1 years

这也意味着下限约为1900.一些库已开始引入64位纪元计数，但目前它们之间相距甚远.

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.