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Subject: [HACKERS] More date time functions
Here are some additional patches mostly related to the date and time
data types. It includes some type conversion routines to move between
the different date types and some other date manipulation routines such
as date_part(units,datetime).
I noticed Edmund Mergl et al's neat trick for getting function overloading
for builtin functions, so started to use that for the date and time stuff.
Later, if someone figures out how to get function overloading directly
for internal C code, then we can move to that technique.
These patches include documentation updates (don't faint!) for the built-in
man page. Doesn't yet include mention of timestamp, since I don't know
much about it and since it may change a bit to become a _real_ ANSI timestamp
which would include parser support for the declaration syntax (what do you
think, Dan?).
The patches were developed on the 970330 release, but have been rebuilt
off of the 970402 release. The first patch below is to get libpq to compile,
on my Linux box, but is not related to the rest of the patches and you can
choose not to apply that one at this time. Thanks in advance, scrappy!
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Subject: [HACKERS] backend/utils/adt/timestamp.c
Back to this timezone stuff. The struct tm has a field (tm_gmtoff) which
is the offset from UTC (GMT is archaic BTW) in seconds. Is this the
value you are looking for when you use timezone? Note that this applies
to NetBSD but it does not appear to be in either ANSI C or POSIX. This
looks like one of those things that is just going to have to be hand
coded for each platform.
Why not just store the values in UTC and use localtime instead of
gmtime when retrieving the value?
Also, you assume the time is returned as a 4 byte integer. In fact,
there is not even any requirement that time be an integral value. You
should use time_t here.
The input function seems unduly restrictive. Somewhere in the sources
there is an input function that allows words for months. Can't we do
the same here?
There is a standard function, difftime, for subtracting two times. It
deals with cases where time_t is not integral. There is, however, a
small performance hit since it returns a double and I don't believe
there is any system currently which uses anything but an integral for
time_t. Still, this is technically the correct and portable thing to do.
The returns from the various comparisons should probably be a bool.
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