SystemTime in std::time - Rust (original) (raw)
Struct SystemTime
1.8.0 · Source
pub struct SystemTime(/* private fields */);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 aSystemTime 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 Durationto indicate that this sort of time drift may happen and needs to be handled.
Although a SystemTime cannot be directly inspected, the UNIX_EPOCHconstant 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.
A SystemTime does not count leap seconds.SystemTime::now()’s behavior around a leap second is the same as the operating system’s wall clock. The precise behavior near a leap second (e.g. whether the clock appears to run slow or fast, or stop, or jump) depends on platform and configuration, so should not be relied on.
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:?}");
}
}
}§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:
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.
1.28.0 · Source
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 existingSystemTime instance can tell how far away from this point in time a measurement lies, and using UNIX_EPOCH + duration can be used to create aSystemTime instance to represent another fixed point in time.
duration_since(UNIX_EPOCH).unwrap().as_secs() returns the number of non-leap seconds since the start of 1970 UTC. This is a POSIX time_t (as a u64), and is the same time representation as used in many Internet protocols.
§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!"),
}1.8.0 · Source
Returns the system time corresponding to “now”.
§Examples
use std::time::SystemTime;
let sys_time = SystemTime::now();1.8.0 · Source
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](../result/enum.Result.html#variant.Ok "variant std::result::Result::Ok")([Duration](struct.Duration.html "struct std::time::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:?}");1.8.0 · Source
Returns the difference from this system time to 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](../result/enum.Result.html#variant.Ok "variant std::result::Result::Ok")([Duration](struct.Duration.html "struct std::time::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);1.34.0 · Source
Returns Some(t) where t is the time self + duration if t can be represented asSystemTime (which means it’s inside the bounds of the underlying data structure), Noneotherwise.
1.34.0 · Source
Returns Some(t) where t is the time self - duration if t 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 the underlying data structure. See SystemTime::checked_add for a version without panic.
The resulting type after applying the + operator.
Tests for self and other values to be equal, and is used by ==.
Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
This method returns an ordering between self and other values if one exists. Read more
Tests less than (for self and other) and is used by the < operator. Read more
Tests less than or equal to (for self and other) and is used by the<= operator. Read more
Tests greater than (for self and other) and is used by the >operator. Read more
Tests greater than or equal to (for self and other) and is used by the >= operator. Read more
The resulting type after applying the - operator.