local-tz-offet return 3600 on Jul 13 in EST

[Takashi Kato]

On Linux, local-tz-offset returns 3600 on Jul 13 in EST. In this period, it should return 7200.

NOTE: if tm_isdst is not set (or 0) then it return 7200 however this behaviour is totally implementation dependent.

[Takashi Kato]

Checking snipet:

#include <stdio.h>
#include <time.h>
#include <stdint.h>
int main()
{
  struct tm localTime;
  struct tm utcTime, *gmt;
  time_t current = time(NULL);
  time_t l;
#ifdef _WIN32
  localtime_s(&localTime, &current);
  l = mktime(&localTime);
  gmtime_s(&utcTime, &l);
#else
  localtime_r(&current, &localTime);
  localTime.tm_mon = 12;
  l = mktime(&localTime);
  gmtime_r(&l, &utcTime);
#endif
  printf("Local time is : %s", asctime(&localTime));
  printf("UTC time is : %s", asctime(&utcTime));
  printf("tm_isdst: utc:%d, local:%d\n", utcTime.tm_isdst, localTime.tm_isdst);
  localTime.tm_isdst = 0;
  printf("offset: %ld\n", (int64_t)mktime(&localTime) - mktime(&utcTime));
  printf("offset: %ld\n", localTime.tm_gmtoff);
  return 0;
}

[Takashi Kato]

Adding localTime.tm_isdst = 0 when it calculates timezone offset.

<<<cset cf3e540>>>