1.8.0[][src]Struct std::time::SystemTime

pub struct SystemTime(_);

A measurement of the system clock, useful for talking to external entities like the file system or other processes.

Distinct from the Instant type, this time measurement is not monotonic. This means that you can save a file to the file system, then save another file to the file system, and the second file has a SystemTime measurement earlier than the first. In other words, an operation that happens after another operation in real time may have an earlier SystemTime!

Consequently, comparing two SystemTime instances to learn about the duration between them returns a Result instead of an infallible Duration to indicate that this sort of time drift may happen and needs to be handled.

Although a SystemTime cannot be directly inspected, the UNIX_EPOCH constant is provided in this module as an anchor in time to learn information about a SystemTime. By calculating the duration from this fixed point in time, a SystemTime can be converted to a human-readable time, or perhaps some other string representation.

The size of a SystemTime struct may vary depending on the target operating system.

Example:

use std::time::{Duration, SystemTime};
use std::thread::sleep;

fn main() {
   let now = SystemTime::now();

   // we sleep for 2 seconds
   sleep(Duration::new(2, 0));
   match now.elapsed() {
       Ok(elapsed) => {
           // it prints '2'
           println!("{}", elapsed.as_secs());
       }
       Err(e) => {
           // an error occurred!
           println!("Error: {:?}", e);
       }
   }
}Run

Underlying System calls

Currently, the following system calls are being used to get the current time using now():

PlatformSystem call
Cloud ABIclock_time_get (Realtime Clock)
SGX[insecure_time usercall]. More information on [timekeeping in SGX]
UNIXclock_gettime (Realtime Clock)
DARWINgettimeofday
VXWorksclock_gettime (Realtime Clock)
WASI__wasi_clock_time_get (Realtime Clock)
WindowsGetSystemTimeAsFileTime

Disclaimer: These system calls might change over time.

Methods

impl SystemTime[src]

pub const UNIX_EPOCH: SystemTime1.28.0[src]

An anchor in time which can be used to create new SystemTime instances or learn about where in time a SystemTime lies.

This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with respect to the system clock. Using duration_since on an existing SystemTime instance can tell how far away from this point in time a measurement lies, and using UNIX_EPOCH + duration can be used to create a SystemTime instance to represent another fixed point in time.

Examples

use std::time::SystemTime;

match SystemTime::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!"),
}Run

pub fn now() -> SystemTime[src]

Returns the system time corresponding to "now".

Examples

use std::time::SystemTime;

let sys_time = SystemTime::now();Run

pub fn duration_since(
    &self,
    earlier: SystemTime
) -> Result<Duration, SystemTimeError>
[src]

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

This function may fail because measurements taken earlier are not guaranteed to always be before later measurements (due to anomalies such as 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 represents the amount of time elapsed from the specified measurement to this one.

Returns an Err if earlier is later than self, and the error contains how far from self the time is.

Examples

use std::time::SystemTime;

let sys_time = SystemTime::now();
let difference = sys_time.duration_since(sys_time)
                         .expect("Clock may have gone backwards");
println!("{:?}", difference);Run

pub fn elapsed(&self) -> Result<Duration, SystemTimeError>[src]

Returns the difference between the clock time when this system time was created, and the current clock time.

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

To measure elapsed time reliably, use Instant instead.

Returns an Err if self is later than the current system time, and the error contains how far from the current system time self is.

Examples

use std::thread::sleep;
use std::time::{Duration, SystemTime};

let sys_time = SystemTime::now();
let one_sec = Duration::from_secs(1);
sleep(one_sec);
assert!(sys_time.elapsed().unwrap() >= one_sec);Run

pub fn checked_add(&self, duration: Duration) -> Option<SystemTime>1.34.0[src]

Returns Some(t) where t is the time self + duration if t can be represented as SystemTime (which means it's inside the bounds of the underlying data structure), None otherwise.

pub fn checked_sub(&self, duration: Duration) -> Option<SystemTime>1.34.0[src]

Returns Some(t) where t is the time self - duration if t can be represented as SystemTime (which means it's inside the bounds of the underlying data structure), None otherwise.

Trait Implementations

impl Add<Duration> for SystemTime[src]

type Output = SystemTime

The resulting type after applying the + operator.

fn add(self, dur: Duration) -> SystemTime[src]

Panics

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

impl AddAssign<Duration> for SystemTime1.9.0[src]

impl Clone for SystemTime[src]

impl Copy for SystemTime[src]

impl Debug for SystemTime[src]

impl Eq for SystemTime[src]

impl Hash for SystemTime[src]

impl Ord for SystemTime[src]

impl PartialEq<SystemTime> for SystemTime[src]

impl PartialOrd<SystemTime> for SystemTime[src]

impl StructuralEq for SystemTime[src]

impl StructuralPartialEq for SystemTime[src]

impl Sub<Duration> for SystemTime[src]

type Output = SystemTime

The resulting type after applying the - operator.

impl SubAssign<Duration> for SystemTime1.9.0[src]

Auto Trait Implementations

impl RefUnwindSafe for SystemTime

impl Send for SystemTime

impl Sync for SystemTime

impl Unpin for SystemTime

impl UnwindSafe for SystemTime

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = !

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.