What is Best way to calculate time span

Question

In my c# program, my requirement is to calculate a timespan for business logic execution that is inside a foreach loop I have to store time span.

I am using following code

for (int i = 0; i < 100; i++)
{
    DateTime start= DateTime.Now; 
    // Business logic
    DateTime end= DateTime.Now; 
    TimeSpan time = start.Subtract(end);
    // Save timespan in log file
}

Please correct me whether I am using right code, or do I need to modify for better performance and result.

Camphorate

I think you would be more interested in Stopwatch – Estellestella

Using DateTime.Now instead of DateTime.UtcNow is almost never the right thing to do (but StopWatch is better in this case anyway). – Bluepencil

Possible duplicate of Is DateTime.Now the best way to measure a function's performance? – Vernettaverneuil

Answer 1

You should use a Stopwatch. The Stopwatch is much more accurate for time measurement than the wall time clock.

var sw = Stopwatch.StartNew();
// business logic
sw.Stop();
TimeSpan time = sw.Elapsed;

Delladelle

Thanks, great information, further two more questions 1. As i am using for loop hence no need to create instance of Stopwatch inside loop everytime (am i right?) 2. I want total time spend in second if less than 1 minute otherwise in minutes if greater than 1 minute, any information on that? – Camphorate

Answer 2

The easiest way would be to:

TimeSpan time = DateTime.Now - start;

Alternatively, you could use a stopwatch which gives more accurate results. See http://msdn.microsoft.com/en-us/library/system.diagnostics.stopwatch.aspx for how to work with a stopwatch.

Ralph

Answer 3

It looks like you're using the timespan to measure performance. Your code is fine, however you should be aware that DateTimes are only so precise (about 10-15ms on most machines -- see the "Useless Timer Mechanism" section here for an explanation).

DateTimes are also not contiguous; what if the first DateTime is retrieved just before daylight savings time kicks in, and the latter one just after? An operation that takes one second could show up as taking an hour, or even negative time. Even with all times in UTC, there's potential problems when the user changes the time manually, or jumps caused by the computer going to sleep and waking up, etc.

A better alternative would be to use the Stopwatch class, which is designed for this sort of thing and uses a high-precision timer internally (via the QueryPerformanceCounter() Win32 function).

Rebatement

Answer 4

To answer your follow up questions, (1) you are correct, you do not need to reinstantiate a StopWatch every iteration. You just need to use the restart method, like so:

Stopwatch sw = new Stopwatch();
sw.Start(); // To initialize
for (int i = 0; i < 100; i++)
{
    sw.Restart();
    // Business logic 
    TimeSpan time = sw.Elapsed;
    // Save timespan in log file
}

(2) You would probably have to write a few lines of code to return the value in seconds if less than one minute, and minutes if greater than, but here would be an example of doing that (assume this is the line right after saving the timespan from the above example):

TimeSpan time = sw.Elapsed;
int iSecondsOrMinutes = time.TotalSeconds < 60 ? time.Seconds : (int)time.TotalMinutes;

This example uses a Ternary Operator to save the integer for the amount of minutes or seconds.

Shultz