Convert GMT to Local time - php

Question

Edit: This function does work in PHP, it isn't working for me within the CakePHP framework which I didn't think relevant when originally posting.
This function takes a string formatted date/time and a local timezone (e.g. 'America/New_York'). It supposed to return time converted to the local timezone. Currently, it does not change.
I pass it: '2011-01-16 04:57:00', 'America/New_York' and I get back the same time I pass in.
function getLocalfromGMT($datetime_gmt, $local_timezone){
$ts_gmt = strtotime($datetime_gmt.' GMT');
$tz = getenv('TZ');
// next two lines seem to do no conversion
putenv("TZ=$local_timezone");
$ret = date('Y-m-j H:i:s',$ts_gmt);
putenv("TZ=$tz");
return $ret;
}
I've seen the references to the new methods for default_timezone_get/set. I'm not currently interested in using that method because I'd like this code to work with older versions of PHP.

Answer 1

Apparently, in CakePHP, if you're using date_default_timezone_set() in your config file, which we are, the TZ environment variable setting method does not work. So, the new version, which seems to work perfectly is:
function __getTimezone(){
if(function_exists('date_default_timezone_get')){
return date_default_timezone_get();
}else{
return getenv('TZ');
}
}
function __setTimezone($tz){
if(function_exists('date_default_timezone_set')){
date_default_timezone_set($tz);
}else{
putenv('TZ='.$tz);
}
}
// pass datetime_utc in a standard format that strtotime() will accept
// pass local_timezone as a string like "America/New_York"
// Local time is returned in YYYY-MM-DD HH:MM:SS format
function getLocalfromUTC($datetime_utc, $local_timezone){
$ts_utc = strtotime($datetime_utc.' GMT');
$tz = $this->__getTimezone();
$this->__setTimezone($local_timezone);
$ret = date('Y-m-j H:i:s',$ts_utc);
$this->__setTimezone($tz);
return $ret;
}

Answer 2

how about this
<?php
// I am using the convention (assumption) of "07/04/2004 14:45"
$processdate = "07/04/2004 14:45";
// gmttolocal is a function
// i am passing it 2 parameters:
// 1)the date in the above format and
// 2)time difference as a number; -5 in our case (GMT to CDT)
echo gmttolocal($processdate,-5);
function gmttolocal($mydate,$mydifference)
{
// trying to seperate date and time
$datetime = explode(" ",$mydate);
// trying to seperate different elements in a date
$dateexplode = explode("/",$datetime[0]);
// trying to seperate different elements in time
$timeexplode = explode(":",$datetime[1]);
// getting the unix datetime stamp
$unixdatetime = mktime($timeexplode[0]+$mydifference,$timeexplode[1],0,$dateexplode[0],$dateexplode[1],$dateexplode[2]);
// return the local date
return date("m/d/Y H:i",$unixdatetime));
}
?>