Hello Everyone, This is Gopesh Kumar Chaudhary from India. I have couple of queries regarding mktime function. e.g. TZ=Europe/Berlin (Olson) struct tm prnt_time; prnt_time.tm_wday = 0; prnt_time.tm_mon = 10 - 1; prnt_time.tm_mday = 30; prnt_time.tm_hour = 2; prnt_time.tm_min = 0; prnt_time.tm_sec = 0; prnt_time.tm_year = 116; prnt_time.tm_isdst = -1; Above tm structure represent 30th OCT 2:30 2016 for Europe/Berlin in Olson . For Europe/Berlin DST fallback will happen on 30th Oct at 3 , so clock will show 2 to 3 time period twice. I have set the dst flag to -1 , for mktime to decide whether the given time in tm structure is DST time or non DST time. Now coming to my query : 1) In above mentioned scenario does mktime has the intelligence to decide whether above mentioned time in tm structure is in DST or not as dst flag is set to -1 ? 2) I have a sample code Sample code :- ----------------------- # cat gops.c #include<stdio.h> #include<time.h> int main(int argc,char **argv){ struct tm *at; time_t when,now; now=atoi(argv[1]); at=localtime(&now); at->tm_isdst = -1; when=mktime(at); printf("now=%d when=%d\n",now,when); return 0; } OS: Linux (RHEL 7.2) Platform:x86 TZ:Europe/Berlin (Olson) # ./gops 1477787940 ==============>This epoch is for 2:39 30th Oct 2016 DST now=1477787940 when=1477791540 ====>Here mktime is giving me the epoch for 2:39 30th Oct 2016 non-DST # ./gops 1477791540 ==============>This epoch is for 2:39 30th Oct 2016 non DST now=1477791540 when=1477791540 ====>Here mktime is giving me the epoch for 2:39 30th Oct 2016 non-DST With the above example it can be seen that irrespective of the DST/non-DST window , it is always giving non DST epoch only ---- Is this standard behavior or is this bug in mktime ? Thanks. Regards, Gopesh Kumar Chaudhary