Getting more accurate time measurement

Question

Currently I'm recording the time between two events in decimal minutes using :

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSCalendarUnit unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSWeekCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSDate *date = [NSDate date];
NSDateComponents *dateComponents =  [calendar components:unitFlags fromDate:date];

CGFloat hour = [dateComponents hour];
CGFloat minute = [dateComponents minute];
CGFloat second = [dateComponents second];

//set start time in decimal minutes
CGFloat startTime = ((hour*3600.0)+(minute*60.0)+(second))*.016666;

//do work...

//set end time in decimal minutes
CGFloat endTime = ((hour*3600.0)+(minute*60.0)+(second))*.016666;

//calculate time elapsed in decimal minutes
CGFloat totalTime = endTime-startTime;

The issue that I'm having is that I am really only getting the time in seconds and then converting to decimal minutes. So, the only values that I'm getting are 0.016663 (one second in decimal minutes), 0.033325 (two seconds in decimal minutes), 0.049988 (three seconds in decimal minutes), etc. I'm not getting any values in between. Is there any way I can get a more accurate time? I checked to see if NSDateComponents has a millisecond property or whatnot, but I couldnt find any.

Thanks!

Answer 1

You can also use CFAbsoluteTimeGetCurrent() which returns a double containing time in seconds and fractions of a second:

CFAbsoluteTime startTime = CFAbsoluteTimeGetCurrent();

Then later you can compute an elapsed time in seconds and fractions of a second:

elapsed = CFAbsoluteTimeGetCurrent() - startTime;

NSLog(@"Elapsed Time: %0.3f seconds", elapsed);

I like to have debug code (#ifdef DEBUG) in my app delegate and in viewDidAppear in my first view controller to report the elapsed startup time so I can keep an eye on that while developing.

Answer 2

Why not just use NSDate?

NSDate *date1, *date2;
NSTimeInterval timeInSeconds;

date1 = [NSDate date];

// Do work

date2 = [NSDate date];
timeInSeconds = [date2 timeIntervalSinceDate:date1];

// Or, without using date2:

timeInSeconds = -[date1 timeIntervalSinceNow];

That should give your measurement sub-second accuracy.

Answer 3

If you want to get Unix-y, you can use gettimeofday (reference):

struct timeval tv;
gettimeofday(&tv, NULL);
NSLog(@"seconds: %d, microseconds: %d\n", tv.tv_sec, tv.tv_usec);

Be sure to add #import <sys/time.h> to your file

Answer 4

Or if you really want to get down the metal, you can use mach_absolute_time(), as per this SO Q/A and/or Apple docs.