>>>>> "Whit" == Whit Armstrong <[EMAIL PROTECTED]>
>>>>> on Wed, 13 Aug 2003 15:23:58 -0400 writes:
Whit> Have you noticed any problems with big dates (>=1/1/2040) in R?
Whit> Here is the bit of code that I'm having trouble with:
>> test.date <- strptime("1/1/2040",format="%m/%d/%Y")
>>
>> unlist(test.date)
Whit> sec min hour mday mon year wday yday isdst
Whit> 0 0 0 1 0 140 0 0 0
>>
>> date.plus.one <- as.POSIXct(test.date) + 24*60*60
>> date.plus.one.lt <- as.POSIXlt(date.plus.one)
>>
>> unlist(date.plus.one.lt)
Whit> sec min hour mday mon year wday yday isdst
Whit> 0 0 0 2 0 140 0 1 0
Whit> Notice that wday (the weekday, 0=Sunday, 7=Saturday) doesn't change.
Whit> Am I missing something?
Probably the "C library millenium bug" (not official name).
The C library standard type for timedates, "time_t", is
"usually" encoded using 32-bit integers, measuring seconds
since the beginning of 1970.
It has been well-known for years that this will lead to integer
overflow from 19 Jan 2038 :
> as.POSIXct(strptime("1/1/1970",format="%m/%d/%Y"))+ .Machine$integer.max
[1] "2038-01-19 03:14:07 CET"
I had thought that the R implementation carefully used doubles
instead of integers everywhere, but I guess we somewhere rely on
system-internal things even here.
For me, on Intel- Linux (RH 7.3, newer gcc) it's even worse:
> unlist(date.plus.one.lt)
sec min hour mday mon year wday yday isdst
0 0 0 2 0 140 6 0 0
~~~~~~~~~
i.e. `wday' has been counted backwards, and `yday' has remained at 0.
-----
I guess we have to wait for 64-bit implementations of "time_t"
or write our own code that works around the many C-library-bugs
we (the R community) have encountered concerning POSIX-time
implementations.
Prof Brian Ripley will know more on this..
Martin Maechler <[EMAIL PROTECTED]> http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum LEO C16 Leonhardstr. 27
ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND
phone: x-41-1-632-3408 fax: ...-1228 <><
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