site_archiver@lists.apple.com Delivered-To: darwin-dev@lists.apple.com I'm using gettimeofday(), on OS X 10.3.6, to get the time resolution I need (milliseconds). If I'm reading the documentation right, I should be getting time in UTC. However, I'm getting local time. This is not what you asked, put just for the correctness of the discussion; Actually, my MacOS X man page says "Greenwich time" and not UTC, and this is in some senses more correct than the latter. I think the man pages for gettimeofday() on the OSes that mention UTC are wrong, as I doubt they will ever return UTC. UTC is a time scale with all seconds equally long. That means it has to be corrected for the variations in the movement of the Earth to keep in sync with the Earth's day and year by inserting or removing leap seconds every now and then. These are inserted just before midnight on June 30 or Dec 31. Since the introduction in 1972, UTC has gotten an extra 22 seconds inserted. In other words, the time 23h 59m 60s has existed 22 times in this time scale. I doubt any implementation of gettimeofday() ever returns time stamps that relates to this time scale (except maybe during the first half of 1972, depending on how you choose to look at it), since it would make all programs' conversion routines have to be updated with when the leap seconds happened, and those have happened every 1.5 year or so. On the other hand, the clock may be synchronized using NTP that actually uses the same second ticks as UTC (except when there are leap seconds which NTP doesn't support so it takes a little while before everything synchs together again), so in the sense gettimeofday kind of returns UTC *ticks*. But gettimeofday still does not return UTC seconds since 1970, rather GMT seconds (or UT, or UT1, or whatever scale you prefer). So - get better timing by don't confusing the time scales! :-) /ragge _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.appl... --On Wed, 1 Dec 2004 17:57:32 -0500 "Michael Rubinstein" <mrubinstein@rai-dev.com> wrote: Should gettimeofday() return local time? This email sent to site_archiver@lists.apple.com