[tz] Irish Standard Time vs Irish Summer Time
eggert at cs.ucla.edu
Fri Jan 19 19:50:53 UTC 2018
On 01/19/2018 06:58 AM, Paul.Koning at dell.com wrote:
> Does POSIX say anything?
POSIX uses different phrases in different places to talk about tm_isdst
and related notions. In its discussion of the TZ environment variable:
it talks about "the alternative (dst -such as Daylight Savings Time)
timezone". In its discussion of time.h:
it says "The value of tm_isdst shall be positive if Daylight Savings
Time is in effect, 0 if Daylight Savings Time is not in effect, and
negative if the information is not available."; this is language taken
directly from the ISO C standard, section 7.27.1.
The language of the C standard is older, and the POSIX language for TZ
was added later, I suppose by a committee that concluded that calling it
"the alternative timezone" would allow more freedom to implementations
for situations where calling it "daylight saving" was inappropriate.
Robert Elz's summary of what tm_isdst was actually used for matches my
impression as well.
More information about the tz