My tests show (with recent glibc version) that with TZ=UTC mktime will return -1 for tm_isdst=1. For tm_isdst=0 and tm_isdst=-1 mktime returns the same value.
IMHO, tm_isdst=0 makes the most sense for TZ=UTC as UTC does not support DST. On Wed, Apr 21, 2021 at 6:50 PM Richard Cochran <richardcoch...@gmail.com> wrote: > On Wed, Apr 21, 2021 at 11:51:55AM +0000, Geva, Erez wrote: > > Looks like the man page is not accurate. > > Looking in > https://pubs.opengroup.org/onlinepubs/009695399/functions/mktime.html > > Okay, I see now, in the man page we read: > > The value specified in the tm_isdst field informs mktime() whether > or > not daylight saving time (DST) is in effect for the time supplied > in > the tm structure: a positive value means DST is in effect; zero > means > that DST is not in effect; and a negative value means that > mktime() > should (use timezone information and system databases to) attempt > to > determine whether DST is in effect at the specified time. > > So the only input values are -1, 0, and 1. > > Can anybody tell me what glibc will do with TZ=UTC ? > > IOW, should tm_isdst be passed as 0 or -1 ? > > Thanks, > Richard >
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