Devs and Time Clock Rollovers
Let’s party like it’s 1999!
You have probably written programs with a bug related to the calculation of time (I certainly have!). For example, you need to work out the number of days there is between two dates, such as between 29 November and 20 December, and calculate:
Days = Date (20,12) — Date (29,11)
and we get 21 days. And you remember that we will have a problem if we calculate over the New Year:
Days = Date (4,1) — Date (29,11)
So we add in the year, and we can determine the right number of days. But many developers just look at the last two digits in the year, and then perform their calculation, so that the days between 1/1/16 and 1/1/19 is three times the number of days in each year. But what happens when we roll over from 2019 to 2020?
Let’s party like it’s 1999!
So, at the start of the 21st Century, we had a problem in that developers had often using the last two digits of the year to perform their time calculations. This caused the Millennium Bug, and where many worried that control systems would crash when the 21st Century arrived. Luckily, the bugs had been mostly identified and it passed without many problems. Developers were told that they should always use system time calls which included the year in their…
