持续时间和计算
Measure the elapsed time between two code sections
Measures time::Instant::elapsed
since time::Instant::now
.
Calling time::Instant::elapsed
returns a time::Duration
that we print at the end of the example.
This method will not mutate or reset the time::Instant
object.
use std::time::{Duration, Instant}; # use std::thread; # # fn expensive_function() { # thread::sleep(Duration::from_secs(1)); # } fn main() { let start = Instant::now(); expensive_function(); let duration = start.elapsed(); println!("Time elapsed in expensive_function() is: {:?}", duration); }
Perform checked date and time calculations
Calculates and displays the date and time two weeks from now using
DateTime::checked_add_signed
and the date of the day before that using
DateTime::checked_sub_signed
. The methods return None if the date and time
cannot be calculated.
Escape sequences that are available for the
DateTime::format
can be found at chrono::format::strftime
.
extern crate chrono; use chrono::{DateTime, Duration, Utc}; fn day_earlier(date_time: DateTime<Utc>) -> Option<DateTime<Utc>> { date_time.checked_sub_signed(Duration::days(1)) } fn main() { let now = Utc::now(); println!("{}", now); let almost_three_weeks_from_now = now.checked_add_signed(Duration::weeks(2)) .and_then(|in_2weeks| in_2weeks.checked_add_signed(Duration::weeks(1))) .and_then(day_earlier); match almost_three_weeks_from_now { Some(x) => println!("{}", x), None => eprintln!("Almost three weeks from now overflows!"), } match now.checked_add_signed(Duration::max_value()) { Some(x) => println!("{}", x), None => eprintln!("We can't use chrono to tell the time for the Solar System to complete more than one full orbit around the galactic center."), } }
Convert a local time to another timezone
Gets the local time and displays it using offset::Local::now
and then converts it to the UTC standard using the DateTime::from_utc
struct method. A time is then converted using the offset::FixedOffset
struct and the UTC time is then converted to UTC+8 and UTC-2.
extern crate chrono; use chrono::{DateTime, FixedOffset, Local, Utc}; fn main() { let local_time = Local::now(); let utc_time = DateTime::<Utc>::from_utc(local_time.naive_utc(), Utc); let china_timezone = FixedOffset::east(8 * 3600); let rio_timezone = FixedOffset::west(2 * 3600); println!("Local time now is {}", local_time); println!("UTC time now is {}", utc_time); println!( "Time in Hong Kong now is {}", utc_time.with_timezone(&china_timezone) ); println!("Time in Rio de Janeiro now is {}", utc_time.with_timezone(&rio_timezone)); }