NSDate incorrect time displayed

What is your locale? What is your timezone?

What locale and timezone does NSDate use by default? (You can look that up in NSDate's class reference doc.)

A one hour difference sounds like a DST issue. Different locales (countries, states, regions) have different rules for when DST goes into effect. Without knowing your locale and timezone, no one knows what rules are being followed in your case.

 

Use a specific NSDateFormatter.

Also read the NSDate class reference doc. The -description method is what %@ uses. Read that. Also read the two other methods whose name starts with "description".

Do you mean GMT as in UTC (which doesn't do DST), or GMT as in Western European Time with DST adjustment?
http://en.wikipedia.org/wiki/Greenwich_Mean_Time

When I asked for locale and timezone, I meant what are your default NSLocale and NSTimeZone objects. Be specific. In particular, is DST in effect or not?

 

The time displayed is correct.
The clock on your wall displays local time, not UTC. Off by one hour.
Your assumption that NSLog should display the local time is wrong.

To make this more clear: If you somewhere in the UK, another programmer in New York, and a third programmer in Los Angeles, run this program at exactly the same time, then you will all see identical output. But if you all three look at your watch at the same moment, the time displayed by your watches will be very different.

 

When I try it, I see local time:

Code:

#import <Foundation/Foundation.h>

int main(int arcgc, char *argv[])
{
	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

	NSDate *now = [NSDate date];
	NSLog(@"%@", now);
	
	[pool drain];
	return 0;
}

I also see a TZ offset. It does the same thing across 10.4, 10.5, 10.6. I don't have a 10.7 at hand to test it on.

Commands to compile and run:

Code:

gcc -std=c99 -framework Foundation now.m -o now
./now

Going back to the OP:

If I change my System Preferences > Date & Time > Time Zone to London ENG, UK, it shows my Time Zone as "British Summer Time". If I move it to Dublin, it shows "Irish Summer Time". If I move it to Iceland, it shows "Greenwich Mean Time", because Iceland doesn't observe DST.

Please post the output from running the above program in Terminal. Also post the output from this Terminal command:

Code:

date

If you're in the UK, and your Time Zone shows as "Greenwich Mean Time" in System Preferences, then I'd guess you have your TZ set wrong. You should pick one of the cities near you that observes one of the Summer Times. Tell us which city it is, so we can duplicate it. And tell us what city it was before changing it. Also tell us exactly which OS version you're using.

 

[NSDate date] doesn't display anything, and isn't in any sense "designed for displaying a local date". It's for creating an NSDate object (NSDate objects do not contain any locale information and have purposes other than display). The -description method on NSDate, which is what %@ uses, is intended for debug/logging use only. Do not rely on it to be in *any* particular format, or for its format to be consistent between machines or OS versions.

 

The NSDate is accurate. The problem you're having is one of formatting: what it prints, not whether the NSDate itself is accurate.

If NSDate has a formatting problem, you have to post the details that allow someone to diagnose the problem. When I asked for things like the exact output from running the program, and the settings in System Preferences (like what you chose as Nearest City), it was to allow someone else to duplicate those settings, in an effort to duplicate the problem. So far, you've posted none of the details, so no one can duplicate the problem, nor begin trying to diagnose its cause.

Also, you originally posted that your time zone was GMT, then you later revised that to BST. Getting accurate details of your setup will be important to solving the problem. We don't even know what OS version you're using, one of the more fundamental details.

You could try creating a new user account, then running the posted NSDate test program there, and seeing if the problem also occurs there. If not, then it's probably a setting specific to your original account. If the problem also occurs in the new user, then it's probably a system-wide setting. Once again, though, complete and accurate details will be needed.