How to round off timestamp in milliseconds to nearest seconds?

Question

How to round off the current timestamp in milliseconds to seconds?

If this is the current timestamp in milliseconds I have -

1384393612958

The if I am rounding off to nearest second then will it be like this?

Time in MS rounded off to nearest Second = 1384393612000

I might need to do this both in Java and C++.

Answer 1

If you are using Python:

old_number = 1384393612958
new_number = 1000 * (old_number / 1000)

print new_number

Basically you want to use an integer number, divide by one thousand (to shave off the milli-seconds), and then multiple by thousand to get the ms value rounded to seconds.

Answer 2

In Java you can use Calendar to something like this:

Calendar cal = Calendar.getInstance().setTimeInMillis(millisec);
int seconds = cal.get(Calendar.SECONDS);

Alternatively (and can work for C++ too) you can do:

int sec = ((millisec + 500) / 1000);

adding 500 ms allows you to round the number properly.

Answer 3

tl;dr

Instant.ofEpochMilli( 1_384_393_612_958L ) 
       .truncatedTo( ChronoUnit.SECONDS )
       .toEpochMilli() 

java.time

The modern approach in Java uses the java.time classes.

The Instant class represents a point on the timeline in UTC with a resolution of nanoseconds.

Instant instant = Instant.ofEpochMilli( 1_384_393_612_958L ) ;
Instant instantTrunc = instant.truncatedTo( ChronoUnit.SECONDS ) ;
long millis = instantTrunc.toEpochMilli() ;