Home Page
  • February 29, 2024, 08:07:43 am *
  • Welcome, Guest
Please login or register.

Login with username, password and session length
Advanced search  

News:

Official site launch very soon, hurrah!


Author Topic: Setting the current time zone through a numeric offset  (Read 8483 times)

Dakusan

  • Programmer Person
  • Administrator
  • Hero Member
  • *****
  • Posts: 529
    • View Profile
    • Dakusan's Domain
Setting the current time zone through a numeric offset
« on: March 23, 2011, 10:54:31 pm »


I had the need today to be able to set the current time zone for an application in multiple computer languages by the hourly offset from GMT/UTC, which turned out to be a lot harder than I expected. It seems most time zone related functions, at least in Linux, expect you to use full location strings to set the current time zone offset (i.e. America/Chicago).


After a lot of research and experimenting, I came up with the following results. All of these are confirmed working in Linux, and most or all of them should work in Windows too.

LanguageFormat NoteFormat for GMT+5Format for GMT-5
CNegateGMT-5GMT5
PerlNegateGMT-5GMT5
SQLRequires Sign+5:00-5:00
PHPNegate, Requires SignEtc/GMT-5Etc/GMT+5

And here are examples of using this in each language. The “TimeZone” string variable should be a 1-2 digit integer with an optional preceding negative sign:
LanguageExample
C

#include <stdio.h> //snprintf
#include <stdlib.h> //setenv, atoi
#include <time.h> //tzset

...

char Buffer[10];
snprintf(Buffer, 10, "GMT%i", -atoi(TimeZone));
setenv("TZ", Buffer, 1);
tzset();
      
Perl

use POSIX qw/tzset/;
$ENV{TZ}='GMT'.(-$TimeZone);
tzset;
      
SQL [Query string created via Perl]

$Query='SET time_zone="'.($TimeZone>=0 ? '+' : '').$TimeZone.':00"';
      
PHP

date_default_timezone_set('Etc/GMT'.($TimeZone<=0 ? '+' : '').(-$TimeZone));
      
Logged