Обсуждение: AW: AW: AW: Re: tinterval - operator problems on AIX

> Oh, so AIX and IRIX have just one-line time zone databases? Yuck.
> 
> How about having some #if BROKEN_TIMEZONE_DATABASE code which uses both
> mktime() and localtime() to derive the correct time zone? That is, call
> mktime to get a time_t, then call localtime() to get the time zone info,
> but only on platforms which do not get a complete result from just the
> call to mktime(). In fact, we *could* check for tm->tm_isdst coming back
> "-1" for every platform, then call localtime() to make a last stab at
> getting a good value.

How would we construct a valid time_t from the struct tm without mktime?

Andreas

> > How about having some #if BROKEN_TIMEZONE_DATABASE code which uses both
> > mktime() and localtime() to derive the correct time zone? That is, call
> > mktime to get a time_t, then call localtime() to get the time zone info,
> > but only on platforms which do not get a complete result from just the
> > call to mktime(). In fact, we *could* check for tm->tm_isdst coming back
> > "-1" for every platform, then call localtime() to make a last stab at
> > getting a good value.
> How would we construct a valid time_t from the struct tm without mktime?

If I understand the info you have given previously, it should be
possible to get a valid tm->tm_isdst by the following sequence of calls:

// call mktime() which might return a "-1" for DST
time = mktime(tm);
// time is now a correct GMT time
// localtime() *is* allowed to return a good tm->tm_isdst
// even for "negative" time_t values.
// I thought I understood this from Andreas' info...
newtm = localtime(time);
// use the new flag for something useful...
dstflag = newtm->tm_isdst;

Yes?
                     - Thomas