#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>


/* Some common time zone name.  */

#if defined _WIN32 && !defined __CYGWIN__
/* Cf. <https://ss64.com/timezones.html>  */
# define FRENCH_TZ  "Romance Standard Time"
#else
/* Cf. <https://en.wikipedia.org/wiki/List_of_tz_database_time_zones>  */
//# define FRENCH_TZ  "Europe/Paris"
# define FRENCH_TZ  "Europe/Berlin"
#endif


static void
show_localtime_result (time_t t)
{
  struct tm *result = localtime (&t);
  printf ("%ld -> %04d-%02d-%02d %02d:%02d:%02d DST=%d\n",
          (long) t,
          result->tm_year + 1900, result->tm_mon + 1, result->tm_mday,
          result->tm_hour, result->tm_min, result->tm_sec,
          result->tm_isdst);
}

int
main (int argc, char *argv[])
{
#if defined _WIN32 && !defined __CYGWIN__
  _putenv ("TZ" "=" FRENCH_TZ);
#else
  setenv ("TZ", FRENCH_TZ, 1);
#endif

  show_localtime_result (1173578399); /* 2007-03-11 02:59:59 */
  show_localtime_result (1173578401); /* 2007-03-11 03:00:01 */

  show_localtime_result (1174784399); /* 2007-03-25 01:59:59 */
  show_localtime_result (1174784401); /* 2007-03-25 03:00:01 */

  return 0;
}
/*
glibc, Cygwin:
1173578399 -> 2007-03-11 02:59:59 DST=0
1173578401 -> 2007-03-11 03:00:01 DST=0
1174784399 -> 2007-03-25 01:59:59 DST=0
1174784401 -> 2007-03-25 03:00:01 DST=1

Native Windows:
1173578399 -> 2007-03-11 01:59:59 DST=0
1173578401 -> 2007-03-11 03:00:01 DST=1
1174784399 -> 2007-03-25 01:59:59 DST=1
1174784401 -> 2007-03-25 02:00:01 DST=1
*/