Struct std::time::SystemTime

1.8.0 · source ·

pub struct SystemTime(_);

Expand description

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

Platform-specific behavior

The precision of SystemTime can depend on the underlying OS-specific time format. For example, on Windows the time is represented in 100 nanosecond intervals whereas Linux can represent nanosecond intervals.

The following system calls are currently being used by now() to find out the current time:

Platform	System call
SGX	insecure_time usercall. More information on timekeeping in SGX
UNIX	clock_gettime (Realtime Clock)
Darwin	gettimeofday
VXWorks	clock_gettime (Realtime Clock)
SOLID	SOLID_RTC_ReadTime
WASI	__wasi_clock_time_get (Realtime Clock)
Windows	GetSystemTimePreciseAsFileTime / GetSystemTimeAsFileTime

Disclaimer: These system calls might change over time.

Note: mathematical operations like add may panic if the underlying structure cannot represent the new point in time.

Implementations

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impl SystemTime

1.28.0 · source

pub const UNIX_EPOCH: SystemTime = UNIX_EPOCH

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年01月01日 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年01月01日 00:00:00 UTC was {} seconds ago!", n.as_secs()),
 Err(_) => panic!("SystemTime before UNIX EPOCH!"),
}

Run

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pub fn now() -> SystemTime

Returns the system time corresponding to "now".

Examples

use std::time::SystemTime;
let sys_time = SystemTime::now();

Run

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

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

Run

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

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 might 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

1.34.0 · source

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

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.

1.34.0 · source

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

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

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impl Add<Duration> for SystemTime

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

Panics

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

type Output = SystemTime

The resulting type after applying the + operator.

1.9.0 · source

impl AddAssign<Duration> for SystemTime

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fn add_assign(&mut self, other: Duration)

Performs the += operation. Read more

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impl Clone for SystemTime

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fn clone(&self) -> SystemTime

Returns a copy of the value. Read more

1.0.0 · source

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more

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impl Debug for SystemTime

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

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impl Hash for SystemTime

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more

1.3.0 · source

fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,

Feeds a slice of this type into the given Hasher. Read more

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impl Ord for SystemTime

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fn cmp(&self, other: &SystemTime) -> Ordering

This method returns an Ordering between self and other. Read more

1.21.0 · source

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values. Read more

1.21.0 · source

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values. Read more

1.50.0 · source

fn clamp(self, min: Self, max: Self) -> Self where
Self: PartialOrd<Self>,

Restrict a value to a certain interval. Read more

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impl PartialEq<SystemTime> for SystemTime

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fn eq(&self, other: &SystemTime) -> bool

This method tests for self and other values to be equal, and is used by ==. Read more

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fn ne(&self, other: &SystemTime) -> bool

This method tests for !=.

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impl PartialOrd<SystemTime> for SystemTime

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fn partial_cmp(&self, other: &SystemTime) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more

1.0.0 · source

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more

1.0.0 · source

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

1.0.0 · source

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more

1.0.0 · source

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

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impl Sub<Duration> for SystemTime

type Output = SystemTime

The resulting type after applying the - operator.

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fn sub(self, dur: Duration) -> SystemTime

Performs the - operation. Read more

1.9.0 · source

impl SubAssign<Duration> for SystemTime

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fn sub_assign(&mut self, other: Duration)

Performs the -= operation. Read more

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impl Copy for SystemTime

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impl Eq for SystemTime

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impl StructuralEq for SystemTime

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impl StructuralPartialEq for SystemTime