iOS: How to measure passed time, independent of clock and time zone changes?

Question

In order to measure the time duration while my app is running, as well as the time that passed while my app was idle in the background, I need a reference clock that is not

Answer 1

#include into your source file.

replace any calls to clock_gettime(CLOCK_MONOTONIC, ×pec_t) with calls to mach_absolute_time().