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

First question，negative integer will implicit cast uint64_t type integer, become a huge positive integer.

Second question, system_clock is a system-wide realtime clock, and if you modified the system time as the system_clock's return time changed. The steady_clock is a physical time so that you can't change it.