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[quote author=Dakusan link=topic=353.msg460#msg460 date=1300935271]
<div class="MainSiteContent"><div style="font-weight:bold;">Original post for <a href="https://www.castledragmire.com/Posts/Setting_the_time_zone_through_a_numeric_offset">Setting the time zone through a numeric offset</a> can be found at <a href="https://www.castledragmire.com/Posts/Setting_the_time_zone_through_a_numeric_offset">https://www.castledragmire.com/Posts/Setting_the_time_zone_through_a_numeric_offset</a>.
Originally posted on: 03/23/11 </div>
<p>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 <b>lot</b> 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).</p>
<p>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.</p><table class="BTable SpaceTable"><tr><th>Language</th><th>Format Note</th><th>Format for GMT+5</th><th>Format for GMT-5</th></tr><tr><td>C</td><td>Negate</td><td>GMT-5</td><td>GMT5</td></tr><tr><td>Perl</td><td>Negate</td><td>GMT-5</td><td>GMT5</td></tr><tr><td>SQL</td><td>Requires Sign</td><td>+5:00</td><td>-5:00</td></tr><tr><td>PHP</td><td>Negate, Requires Sign</td><td>Etc/GMT-5</td><td>Etc/GMT+5</td></tr></table>
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:<table class="BTable SpaceTable"><tr><th>Language</th><th>Example</th></tr><tr><td>C</td><td><pre class=code>
#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();
		</pre></td></tr><tr><td>Perl</td><td><pre class=code>
use POSIX qw/tzset/;
$ENV{TZ}='GMT'.(-$TimeZone);
tzset;
		</pre></td></tr><tr><td>SQL [Query string created via Perl]</td><td><pre class=code>
$Query='SET time_zone="'.($TimeZone>=0 ? '+' : '').$TimeZone.':00"';
		</pre></td></tr><tr><td>PHP</td><td><pre class=code>
date_default_timezone_set('Etc/GMT'.($TimeZone<=0 ? '+' : '').(-$TimeZone));
		</pre></td></tr></table></div>
[/quote]

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Topic Summary

Posted by: Dakusan

« on: March 23, 2011, 10:54:31 pm »

Insert Quote

Original post for Setting the time zone through a numeric offset can be found at https://www.castledragmire.com/Posts/Setting_the_time_zone_through_a_numeric_offset.
Originally posted on: 03/23/11

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.

Language	Format Note	Format for GMT+5	Format for GMT-5
C	Negate	GMT-5	GMT5
Perl	Negate	GMT-5	GMT5
SQL	Requires Sign	+5:00	-5:00
PHP	Negate, Requires Sign	Etc/GMT-5	Etc/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:

Language	Example
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));

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