mod.sources posting; mktime

Wed Jul 13 23:14:41 UTC 2011

I've passed on new time zone stuff to some other folks on the list;
after their editing, the stuff should be posted to mod.sources.
It will (in all probability) include "food for thought" code for
six (count 'em, six) functions for turning time_t's into struct tm's and back:

	struct tm * localtime(time_t t)
	struct tm * gmtime(time_t t)
	struct tm * offtime(time_t t, long offset)

	time_t timelocal(struct tm * tmp)
	time_t timegm(struct tm * tmp)
	time_t timeoff(struct tm * tmp, long offset)

localtime and gmtime are our old friends.  offtime is like gmtime except that
the given offset (in seconds) is used in generating the return value.
(You want to do this, rather than adding the offset to the time and calling
gmtime, to avoid overflow problems at near-minimum and near-maximum time_t
values.)  timelocal, timegm, and timeoff "invert" their counterparts
(well, actually, they just try to do an adequate job).

The troff-ish assumption with localtime and timelocal is that "the same
local time conversion rules must still (or again) be in effect" when timelocal
is called as were in effect when localtime was called to get the "right"

None of the inverting functions gives a hoot about tm_isdst.

There's surely a better way to do things.


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