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Windows (3.1/9X/ME/2K/XP) Daylight Savings behaviour

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Hi, I need some confirmation on the behaviour of windows during a Daylight Savings crossover. If the time is changed under Windows (XP - for sure) it alters the system (BIOS) clock. However, I don''t know what windows does at the Spring and Autumn DS Crossover. It''s not logical for Windows to change the system clock, as other OS''es will not know the clock has been adjusted, and may repeat the operation. So, does windows jog the time to allow for DS internally? and what time does the MSVC 6.0 {ULONG time(NULL);} funtion return, system BIOS time, or windows time? From the MSDN docs... "The time function returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, coordinated universal time, according to the system clock." ... does this mean the number returned by {time(NULL;} is not affected by DS? Thanks, R
ToDoList | Wayout | ManillaPush | SendToSync

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possibly it rather sets an "in-summer-time" flag in the bios.. dunno.. wich other os'' look at and say oh, its yet set..

i have no clue, but that would at least be a solution:D

"take a look around" - limp bizkit
www.google.com

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Windows sets the bios clock. I''ve experienced this on my XP/RedHat box. It probably (and likely) also sets a registry key to ''remember'' that the change occurred.

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Thanks daveperman,

There is a flag set in the 'tstruct' structure of {_ftime(tstruct);}. I'm thinking of using this, but if the BIOS is already changed, then the variable is irrelevant.

Thanks Nik02,

Thanks for the confirmaion, surely that philosophy is a bit dangerous (and unsociable!), esp. if there are more than two users who don't know wether the other has adjusted the clock, and it get's adjusted twice!

I need some more (official) confirmation though... I'll try to look around the internet.

R



ToDoList | Wayout | ManillaPush | SendToSync


[edited by - reaction on September 1, 2003 3:17:09 PM]

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I believe that the ''changed'' flag is per-windows, and not per-user. Of course this only works if both users use the same OS (windows) in the first place!

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I have contacted IBM regarding this problem.

What is reuired are two clocks, wth the second offset from the first; and the first constant.

R

payphone - got to go

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quote:
Original post by reaction
It''s not logical for Windows to change the system clock, as other OS''es will not know the clock has been adjusted, and may repeat the operation.


A bit naive, are we?

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quote:
So, does windows jog the time to allow for DS internally?

It is supposed to.

quote:
and what time does the MSVC 6.0 {ULONG time(NULL);} funtion return, system BIOS time, or windows time?

Why not try it and find out?

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Windows changes the BIOS clock. I had Windows 98 and Windows XP dual-booted, and last April I found my computer''s clock an hour behind (or an hour ahead?) But both of the OSs changed the clock.

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