Difference between steady_clock vs system_clock?

Question

I am trying to see whether my data is 120 second old or not by looking at the timestamp of the data so I have below code:

uint64_t now = duration_cast

        

Answer 1

1. steady_clock uses the system startup time as its epoch, system_clock uses 1970-1-1 00:00 as its epoch, so there is no way to do any math between them, this makes no sense.

2. Before doing any subtraction between 2 unsigned integers, please make sure the minuend is larger than the subtrahend.