Michael Enright <mike <at> kmcardiff.com> writes: > The tznam is set from the tmzone member and when this happens that > member is garbage. This member is garbage POSSIBLY because of a > configuration option in libmozjs. The calling code is in prmjtime.cpp > fills in a struct tm from Spidermonkey's own broken-down time > structure, 'a', and then if the configuration enables, it makes > *another* struct tm with more fields filled in in order to get > a.tm_zone's proper value. My guess is that the path is not enabled but > the bits delivered to me do not disclose whether this righteous code > path is enabled. __cygwin_gettzname is evidently compiled to expect > the tm_zone member to exist because GDB shows it does exist. > > So did any aspect of this change recently? The application and library > were getting along okay before I did cygwin updates. The last time I > had tried to run this code was early June, at which time I was running > it dozens of times a day. > > Also it appears that the tm_zone member is an extension. I haven't > been able to find POSIX guidance about how applications are supposed > use struct tm in compliance in the presence of implementation-defined > fields. POSIX example code shows a usage that does access the 'at > least' fields. The language allows for implementation-defined fields. > No mechanism is provided within POSIX to allow an application to > discover additional fields and take care of them. It seems to me that > an application can then assume that when it provides a struct tm as > input, filling in the time and date reasonably, it is always > sufficient to fill in the 'at least' fields and the implementation is > the one who has to assume that the rest of the fields might not be > filled in.
Two problems I have encountered in the past with manually constructed struct tm: - failing to set struct tm.tm_isdst member to -1, or any negative value, so that mktime(3) will determine whether DST is in effect, and set the struct tm.tzname array from the tzdb - failing to call mktime(3) for each struct tm variable to normalize the struct tm members, determine if DST is in effect if struct tm.tm_isdst member is -1, and set the struct tm.tzname array from the tzdb. Check back in the code to see if struct tm.tm_isdst is set and to what value, and if mktime(3) is called on each struct tm after it is filled. - failing to call mktime() -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
