php - Why do timestamps have a limit to 2038?

Question

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)?

Answer 1

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

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.