The Flow Of time()

• Time always advances, unless the timezone makes it jump backwards (e.g. switch from daylight saving time), or unless the system clock is set abroptly via a 'date' command or similar.
• Thus, we should be careful about how we manage time calculations in code (e.g. never assume that a future time minus a past time gives a meaningful result).
• We check the time with:
  • time(NULL) - returns the number of seconds elapsed since 1/1/1970 at midnight, in UTC.
  • localtime() - translates a given time based on the time zone. returns the time broken into its parts - year, month, day, hour...
    note: the 'month' field is 0-11, not 1-12.
    note 2: the 'year' field is the distance from 1900, not the full year (so year 2005 is represented as 105).
  • mktime() - does the inverse of localtime, with the addition of strange handling of 'out-of-range' values in the various fields (see the man page...)

Originally written by guy keren