On 2014-01-18 10:21, Poul-Henning Kamp wrote: > In message <52da845e.4000...@hfx.eastlink.ca>, "Eric R. Smith" writes: > >>> As you are no doubt aware, the POSIX time_t does not do that. >> >> Doesn't it? If POSIX time_t were in fact a count of SI seconds since the >> epoch then the nature of the "leap second problem" would be quite >> different. time_t uses at least the concept of "day". > > No, in fact it doesn't, it just counts seconds, one after the other. >
Except leap seconds. That's a pretty important "except" for the purposes of this list! > The reason why leapseconds is a problem is that people assume that > it *also* counts minutes, hours and days also. My version of the POSIX standard is a bit old, but it basically defines time_t in terms of days, hours, minutes, and seconds: "A Coordinated Universal Time name (specified in terms of seconds, minutes, hours, days since January 1 of the year, and calendar year minus 1900) is related to a time represented as seconds since the epoch according to the expression below. ... [time_t =] tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 + (tm_year-70)*31536000 + ((tm_year-69)/4)*86400" AFAIK the only change to this in later POSIX standards is that the leap year calculation was fixed. So the "seconds" that time_t counts are defined in terms of days and years, and are not in fact SI seconds. In the rationale there is a discussion of leap seconds, including the charming statement: "...most systems are probably not synchronized to any standard time reference. Therefore, it is inappropriate to require that a time represented as seconds since the Epoch precisely represent the number of seconds between the referenced time and the Epoch." _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
