Setting 'struct tm' tm_zone="GMT" doesn't work, takes default system timezone

Dear Dev-Meisters,

I'm trying to find out why setting tm_zone="GMT" in a "struct tm" is not working on Mac OS X 10.6.x. and mktime()....

However with gmtime() it works but apparently it's not recommended for Mac OS X...

I need to read in a data file with large datasets which contains date / time along with data.

Every date/time (can be about > 500000 lines) is converted to a time_t data structure to find out if there a gaps between dates.

However setting the structure "struct tm" with tm_zone="GMT" doesn't set it to GMT.

It always takes Mac OS X default time zone defined in the Sys Preferences.

I made succesful tests with "NSDate timeIntervalSince1970" (when setting the NSTimezone to GMT): this gives the correct GMT time...

Since > 500000 lines is a little bit overkill performance wise to always create an object I would prefer to use UNIX time stamp...

/* Test for 24 Feb. 2005 at 17h20:10 / Should return: 1109265610 as UTC time */

time_t currentTime;

struct tm myTm;

myTm.tm_year = 2005-1900; // need to subtract -1900

myTm.tm_mon = 2-1; // need to subtract -1 (since month: 0-11)

myTm.tm_mday = 24;

myTm.tm_hour = 17;

myTm.tm_min = 20;

myTm.tm_sec = 10;

myTm.tm_zone = "GMT";

myTm.tm_isdst = 0; // DayLight Saving Time flag = 0 = Off

myTm.tm_gmtoff = 0;

currentTime = mktime(&myTm);

Result on Mac OS X: 1109262010 !! Wrong result: -3600 seconds, should be 1109265610

However using:

currentTime = gmtime(&myTm);

gives the right result: 1109265610

Any suggestions is greatly appreciated