An anchor in time which can be used to create newSystemTime instances orlearn about where in time aSystemTime lies.

This constant is defined to be “1970-01-01 00:00:00 UTC” on all systems withrespect to the system clock. Usingduration_since on an existingSystemTime instance can tell how far away from this point in time ameasurement lies, and usingUNIX_EPOCH + duration can be used to create aSystemTime instance to represent another fixed point in time.

duration_since(UNIX_EPOCH).unwrap().as_secs() returnsthe number of non-leap seconds since the start of 1970 UTC.This is a POSIXtime_t (as au64),and is the same time representation as used in many Internet protocols.

§Examples

usestd::time::SystemTime;matchSystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {Ok(n) =>println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),Err(_) =>panic!("SystemTime before UNIX EPOCH!"),}

Returns the system time corresponding to “now”.

§Examples

usestd::time::SystemTime;letsys_time = SystemTime::now();

Returns the amount of time elapsed from an earlier point in time.

This function may fail because measurements taken earlier are notguaranteed to always be before later measurements (due to anomalies suchas the system clock being adjusted either forwards or backwards).Instant can be used to measure elapsed time without this risk of failure.

If successful,Ok(Duration) is returned where the duration representsthe amount of time elapsed from the specified measurement to this one.

Returns anErr ifearlier is later thanself, and the errorcontains how far fromself the time is.

§Examples

usestd::time::SystemTime;letsys_time = SystemTime::now();letnew_sys_time = SystemTime::now();letdifference = new_sys_time.duration_since(sys_time)    .expect("Clock may have gone backwards");println!("{difference:?}");

Returns the difference from this system time to thecurrent clock time.

This function may fail as the underlying system clock is susceptible todrift and updates (e.g., the system clock could go backwards), so thisfunction might not always succeed. If successful,Ok(Duration) isreturned where the duration represents the amount of time elapsed fromthis time measurement to the current time.

To measure elapsed time reliably, useInstant instead.

Returns anErr ifself is later than the current system time, andthe error contains how far from the current system timeself is.

§Examples

usestd::thread::sleep;usestd::time::{Duration, SystemTime};letsys_time = SystemTime::now();letone_sec = Duration::from_secs(1);sleep(one_sec);assert!(sys_time.elapsed().unwrap() >= one_sec);

ReturnsSome(t) wheret is the timeself + duration ift can be represented asSystemTime (which means it’s inside the bounds of the underlying data structure),Noneotherwise.

ReturnsSome(t) wheret is the timeself - duration ift can be represented asSystemTime (which means it’s inside the bounds of the underlying data structure),Noneotherwise.

§Panics

This function may panic if the resulting point in time cannot be represented by theunderlying data structure. SeeSystemTime::checked_add for a version without panic.

Returns the argument unchanged.

CallsU::from(self).

That is, this conversion is whatever the implementation ofFrom<T> for U chooses to do.