How can I get a precise time, for example in milliseconds in objective-c?

Question

Is there an easy way to get a time very precisely? I need to calculate some delays between method calls. More particular, I want to calculate the speed of scrolling in an UIScrollView.

Answer 1

CFAbsoluteTimeGetCurrent() returns the absolute time as a double value, but I don't know what its precision is -- it might only update every dozen milliseconds, or it might update every microsecond, I don't know.

Answer 2

Does this link (dead now) help? It suggests to use timeIntervalSinceReferenceDate which seems to be at least accurate for milliseconds.

Answer 3

NSDate and the timeIntervalSince* methods will return a NSTimeInterval which is a double with sub-millisecond accuracy. NSTimeInterval is in seconds, but it uses the double to give you greater precision.

In order to calculate millisecond time accuracy, you can do:

// Get a current time for where you want to start measuring from
NSDate *date = [NSDate date];

// do work...

// Find elapsed time and convert to milliseconds
// Use (-) modifier to conversion since receiver is earlier than now
NSTimeInterval timePassed_ms = [date timeIntervalSinceNow] * -1000.0;

Documentation on timeIntervalSinceNow can be found here

There are many other ways to calculate this interval using NSDate, and I would recommend looking at the class documentation for NSDate which is found here

Answer 4

mach_absolute_time() can be used to get precise measurements.

See http://developer.apple.com/qa/qa2004/qa1398.html