Objective-C

Timing

To roughly measure the time necessary to do a certain action:

 CFTimeInterval startTime = CFAbsoluteTimeGetCurrent();
 CFTimeInterval duration = CFAbsoluteTimeGetCurrent() - startTime;
 NSLog(@"Parse time: %f seconds", duration);

This is easier than using mach_absolute_time(), because if you want human-readable time, that function its return value has to be converted (to seconds or what have you).

Edit: for more information on this topic, see Benchmarking on NSHipster.

Note that you are not allowed to use mach_absolute_time() in App Store code.

Debugging

The following standard timestamp is really useful for logging the full time:

 NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
 [dateFormatter setDateFormat:@"dd/MM/yyyy HH:mm:ss"];
 NSString *timestamp = [dateFormatter stringFromDate:[NSDate date]];

One-liners

To get the current second:

      int sec = [[[NSCalendar currentCalendar] components:NSSecondCalendarUnit fromDate:[NSDate date]] second];