On 2017-12-10 22:16, Paul Eggert wrote:
Michael H Deckers via tz wrote:
The definition of the tm_isdst flag does not even mention standard time True, but other parts of POSIX make it clear that when tm_isdst is zero, standard time is intended. See: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_... and look at the TZ environment variable: POSIX says that its first few letters correspond to standard time and that later letters correspond to daylight saving time.
They actually say that the alternative time zone is in effect, such as for DST. So tm_isdst actually means the alternative non-standard time zone "tm_isalt" and not necessarily DST per se.
any dictionary tells us that daylight-saving time is advanced, and not retarded, over the time used otherwise Although that's typical I doubt whether we can take it as an axiom, as POSIX clearly allows DST to be retarded. Also, multiple sources talk about having standard time in summer and daylight-saving time in winter. See: https://en.wikipedia.org/wiki/Winter_time_(clock_lag)
That could be usefully cross-referenced to the relevant zones or rules. I can see headaches coming for testers and implementers who did not allow for those cases! -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada