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I have a time::Duration. How can I get the number of milliseconds represented by this duration as an integer? There used to be a num_milliseconds() function, but it is no longer available.

Shepmaster
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Kevin Burke
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3 Answers3

6

Since Rust 1.33.0, there is an as_millis() function:

use std::time::SystemTime;

fn main() {
    let now = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).expect("get millis error");
    println!("now millis: {}", now.as_millis());
}

Since Rust 1.27.0, there is a subsec_millis() function:

use std::time::SystemTime;

fn main() {
    let since_the_epoch = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).expect("get millis error");
    let seconds = since_the_epoch.as_secs();
    let subsec_millis = since_the_epoch.subsec_millis() as u64;
    println!("now millis: {}", seconds * 1000 + subsec_millis);
}

Since Rust 1.8, there is a subsec_nanos function:

let in_ms = since_the_epoch.as_secs() * 1000 +
            since_the_epoch.subsec_nanos() as u64 / 1_000_000;

See also:

Shepmaster
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iceqing
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  • What does Rust 2018 have to do with the problem? Why are you using `SystemTime` instead of directly using a `Duration`? – Shepmaster Dec 31 '18 at 14:25
  • New to Rust; what advantage do the solutions above have over the simpler: `duration.as_secs_f64() * 1000f64`? It's much more precise than `duration.as_millis()` (ie. it gives me results like `6.716969ms` rather than just an integer), while being simpler than the other two options. – Venryx Mar 28 '22 at 16:21
4

Here is the solution I came up with, which is to multiply the seconds by a billion, add it to the nanoseconds, then divide by 1e6.

let nanos = timeout_duration.subsec_nanos() as u64;
let ms = (1000*1000*1000 * timeout_duration.as_secs() + nanos)/(1000 * 1000);
Kevin Burke
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    I'd rather multiply seconds by 1000, then add `nanos/1000000`. Less risk of overflow. – llogiq Apr 24 '16 at 10:22
  • `subsec_nanos` doesn't return the number of elapsed nanoseconds. It represents the precision of the Duration. – w.brian Mar 13 '17 at 01:15
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    @w.brian the example in the documentation https://doc.rust-lang.org/std/time/struct.Duration.html#method.subsec_nanos supports the facts that the method returns the fractional part of the duration in nanoseconds, so the answer seems correct to me. – poros Jan 30 '18 at 18:32
2

Use time::Duration from the time crate on crates.io which provides a num_milliseconds() method.

aeveris
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