localtime() returning ambigious

Question

I wrote the below code and tested it out on different platforms. I got different results on HP-UX IA64,as compared to other platforms.

Code:

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

int main(void)
{
    time_t t;
    struct tm *gmt, *lat, ldummy;

    tzset();

    printf("Local timezone: TZ=%s\n\n", getenv("TZ"));

    t = 1394881705;

    lat = localtime(&t);
    printf("Local time is : %s", asctime(lat));

    gmt = gmtime(&t);
    printf("GMT is        : %s", asctime(gmt));

    return 0;
}

OUTPUT:-

Linux

$ ./a.out
Local timezone: TZ=CET

Local time is : Sat Mar 15 12:08:25 2014
GMT is        : Sat Mar 15 11:08:25 2014

SunOs

$ ./a.out
Local timezone: TZ=CET

Local time is : Sat Mar 15 12:08:25 2014
GMT is        : Sat Mar 15 11:08:25 2014

AIX

$ ./a.out  
Local timezone: TZ=CET

Local time is : Sat Mar 15 12:08:25 2014
GMT is        : Sat Mar 15 11:08:25 2014

(This is where the problem is) HP-UX IA64

$ ./a.out
Local timezone: TZ=CET

Local time is : Sat Mar 15 11:08:25 2014
GMT is        : Sat Mar 15 11:08:25 2014

I am trying to understand why the output is differing in case of HP-UZ IA64(Version is 11.31). I could not find any relevant documentation for this eccentric behaviour. Would someone help me with understanding this?

Answer 1

On HP-UX ia64, when I provide set timezone as, TZ=CET, it simply considers it as being the same as UTC. As per HP-UX documentation at link emphasis mine, "TZ can be set using the format: [:]STDoffset[DST[offset][,rule]]" The offset here is mandatory and represents "the value that must be added to local time to arrive at Coordinated Universal Time (UTC)."
So, without offset, HP-UX considers the STD the same as UTC.