Daylight Savings Time Madness

[Stefan Raspl <raspl at linux dot vnet dot ibm dot com>]

Debugging a problem related to daylight savings time, I encountered
a very odd behavior. The oddity was reproduced with both, glibc 2.5
and current CVS, and reproduced consistently on i386, PowerPC and
s390. I figure it is essential that you set your timezone to
something other than UTC.
Here's the code:

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

void process(const char *str) {
  struct tm tm, *p_tm;
  char buf[255];
  time_t t;

  printf("starting out with    : %s\n", str);
  strptime(str, "%Y-%m-%d %H:%M:%S", &tm);
  t = mktime(&tm);
  p_tm = localtime(&t);
  strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", p_tm);

  printf("after reconverting   : %s\n", buf);
}

int main() {
  process("2009-04-02 13:35:00");
  sleep(1); // [1]
  process("2009-02-02 13:35:00");

  return 0;
}

When run as is, I get the following output:

	starting out with    : 2009-04-02 13:35:00
	after reconverting   : 2009-04-02 13:35:00
	starting out with    : 2009-02-02 13:35:00
	after reconverting   : 2009-02-02 13:35:00

Now remove the sleep(1) at [1] and run again:

	starting out with    : 2009-04-02 13:35:00
	after reconverting   : 2009-04-02 13:35:00
	starting out with    : 2009-02-02 13:35:00
	after reconverting   : 2009-02-02 12:35:00

Note that the final timestamp is 12:35 instead of 13:35.
Any ideas why a sleep(1) makes a difference?

Ciao,
Stefan

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