# Crate chrono [−] [src]

# Chrono: Date and Time for Rust

It aims to be a feature-complete superset of the time library. In particular,

- Chrono strictly adheres to ISO 8601.
- Chrono is timezone-aware by default, with separate timezone-naive types.
- Chrono is space-optimal and (while not being the primary goal) reasonably efficient.

There were several previous attempts to bring a good date and time library to Rust, which Chrono builds upon and should acknowledge:

- Initial research on the wiki
- Dietrich Epp’s datetime-rs
- Luis de Bethencourt’s rust-datetime

Any significant changes to Chrono are documented in the `CHANGELOG.md` file.

## Usage

Put this in your `Cargo.toml`:

    [dependencies]
    chrono = "0.4"

### Features

Chrono supports various runtime environments and operating systems, and has several features that may be enabled or disabled.

Default features:

- `alloc`: Enable features that depend on allocation (primarily string formatting)
- `std`: Enables functionality that depends on the standard library. This is a superset of `alloc` and adds interoperation with standard library types and traits.
- `clock`: enables reading the system time (`now`), independent of whether `std::time::SystemTime` is present, depends on having a libc.

Optional features:

- `wasmbind`: Enable integration with wasm-bindgen and its `js-sys` project
- `serde`: Enable serialization/deserialization via serde.
- `unstable-locales`: Enable localization. This adds various methods with a `_localized` suffix. The implementation and API may change or even be removed in a patch release. Feedback welcome.

See the cargo docs for examples of specifying features.

## Overview

### Duration

Chrono currently uses its own `Duration` type to represent the magnitude of a time span. Since this has the same name as the newer, standard type for duration, the reference will refer this type as `OldDuration`.

Note that this is an “accurate” duration represented as seconds and nanoseconds and does not represent “nominal” components such as days or months.

When the `oldtime` feature is enabled, `Duration` is an alias for the `time::Duration` type from v0.1 of the time crate. time v0.1 is deprecated, so new code should disable the `oldtime` feature and use the `chrono::Duration` type instead. The `oldtime` feature is enabled by default for backwards compatibility, but future versions of Chrono are likely to remove the feature entirely.

Chrono does not yet natively support the standard `Duration` type, but it will be supported in the future. Meanwhile you can convert between two types with `Duration::from_std` and `Duration::to_std` methods.

### Date and Time

Chrono provides a `DateTime` type to represent a date and a time in a timezone.

For more abstract moment-in-time tracking such as internal timekeeping that is unconcerned with timezones, consider `time::SystemTime`, which tracks your system clock, or `time::Instant`, which is an opaque but monotonically-increasing representation of a moment in time.

`DateTime` is timezone-aware and must be constructed from the `TimeZone` object, which defines how the local date is converted to and back from the UTC date. There are three well-known `TimeZone` implementations:

- `Utc` specifies the UTC time zone. It is most efficient.

- `Local` specifies the system local time zone.

- `FixedOffset` specifies an arbitrary, fixed time zone such as UTC+09:00 or UTC-10:30. This often results from the parsed textual date and time. Since it stores the most information and does not depend on the system environment, you would want to normalize other `TimeZone`s into this type.

`DateTime`s with different `TimeZone` types are distinct and do not mix, but can be converted to each other using the `DateTime::with_timezone` method.

You can get the current date and time in the UTC time zone (`Utc::now()`) or in the local time zone (`Local::now()`).

    use chrono::prelude::*;

    let utc: DateTime<Utc> = Utc::now();       // e.g. `2014-11-28T12:45:59.324310806Z`
    let local: DateTime<Local> = Local::now(); // e.g. `2014-11-28T21:45:59.324310806+09:00`

Alternatively, you can create your own date and time. This is a bit verbose due to Rust’s lack of function and method overloading, but in turn we get a rich combination of initialization methods.

    use chrono::prelude::*;
    use chrono::offset::LocalResult;

    let dt = Utc.ymd(2014, 7, 8).and_hms(9, 10, 11); // `2014-07-08T09:10:11Z`
    // July 8 is 188th day of the year 2014 (`o` for "ordinal")
    assert_eq!(dt, Utc.yo(2014, 189).and_hms(9, 10, 11));
    // July 8 is Tuesday in ISO week 28 of the year 2014.
    assert_eq!(dt, Utc.isoywd(2014, 28, Weekday::Tue).and_hms(9, 10, 11));

    let dt = Utc.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12); // `2014-07-08T09:10:11.012Z`
    assert_eq!(dt, Utc.ymd(2014, 7, 8).and_hms_micro(9, 10, 11, 12_000));
    assert_eq!(dt, Utc.ymd(2014, 7, 8).and_hms_nano(9, 10, 11, 12_000_000));

    // dynamic verification
    assert_eq!(Utc.ymd_opt(2014, 7, 8).and_hms_opt(21, 15, 33),
               LocalResult::Single(Utc.ymd(2014, 7, 8).and_hms(21, 15, 33)));
    assert_eq!(Utc.ymd_opt(2014, 7, 8).and_hms_opt(80, 15, 33), LocalResult::None);
    assert_eq!(Utc.ymd_opt(2014, 7, 38).and_hms_opt(21, 15, 33), LocalResult::None);

    // other time zone objects can be used to construct a local datetime.
    // obviously, `local_dt` is normally different from `dt`, but `fixed_dt` should be identical.
    let local_dt = Local.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12);
    let fixed_dt = FixedOffset::east(9 * 3600).ymd(2014, 7, 8).and_hms_milli(18, 10, 11, 12);
    assert_eq!(dt, fixed_dt);

Various properties are available to the date and time, and can be altered individually. Most of them are defined in the traits `Datelike` and `Timelike` which you should `use` before. Addition and subtraction is also supported. The following illustrates most supported operations to the date and time:

    use chrono::prelude::*;
    use chrono::Duration;

    // assume this returned `2014-11-28T21:45:59.324310806+09:00`:
    let dt = FixedOffset::east(9*3600).ymd(2014, 11, 28).and_hms_nano(21, 45, 59, 324310806);

    // property accessors
    assert_eq!((dt.year(), dt.month(), dt.day()), (2014, 11, 28));
    assert_eq!((dt.month0(), dt.day0()), (10, 27)); // for unfortunate souls
    assert_eq!((dt.hour(), dt.minute(), dt.second()), (21, 45, 59));
    assert_eq!(dt.weekday(), Weekday::Fri);
    assert_eq!(dt.weekday().number_from_monday(), 5); // Mon=1, ..., Sun=7
    assert_eq!(dt.ordinal(), 332); // the day of year
    assert_eq!(dt.num_days_from_ce(), 735565); // the number of days from and including Jan 1, 1

    // time zone accessor and manipulation
    assert_eq!(dt.offset().fix().local_minus_utc(), 9 * 3600);
    assert_eq!(dt.timezone(), FixedOffset::east(9 * 3600));
    assert_eq!(dt.with_timezone(&Utc), Utc.ymd(2014, 11, 28).and_hms_nano(12, 45, 59, 324310806));

    // a sample of property manipulations (validates dynamically)
    assert_eq!(dt.with_day(29).unwrap().weekday(), Weekday::Sat); // 2014-11-29 is Saturday
    assert_eq!(dt.with_day(32), None);
    assert_eq!(dt.with_year(-300).unwrap().num_days_from_ce(), -109606); // November 29, 301 BCE

    // arithmetic operations
    let dt1 = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
    let dt2 = Utc.ymd(2014, 11, 14).and_hms(10, 9, 8);
    assert_eq!(dt1.signed_duration_since(dt2), Duration::seconds(-2 * 3600 + 2));
    assert_eq!(dt2.signed_duration_since(dt1), Duration::seconds(2 * 3600 - 2));
    assert_eq!(Utc.ymd(1970, 1, 1).and_hms(0, 0, 0) + Duration::seconds(1_000_000_000),
               Utc.ymd(2001, 9, 9).and_hms(1, 46, 40));
    assert_eq!(Utc.ymd(1970, 1, 1).and_hms(0, 0, 0) - Duration::seconds(1_000_000_000),
               Utc.ymd(1938, 4, 24).and_hms(22, 13, 20));

### Formatting and Parsing

Formatting is done via the `format` method, which format is equivalent to the familiar `strftime` format.

See `format::strftime` documentation for full syntax and list of specifiers.

The default `to_string` method and `{:?}` specifier also give a reasonable representation. Chrono also provides `to_rfc2822` and `to_rfc3339` methods for well-known formats.

Chrono now also provides date formatting in almost any language without the help of an additional C library. This functionality is under the feature `unstable-locales`:

    chrono { version = "0.4", features = ["unstable-locales"]

The `unstable-locales` feature requires and implies at least the `alloc` feature.

    use chrono::prelude::*;

    let dt = Utc.ymd(2014, 11, 28).and_hms(12, 0, 9);
    assert_eq!(dt.format("%Y-%m-%d %H:%M:%S").to_string(), "2014-11-28 12:00:09");
    assert_eq!(dt.format("%a %b %e %T %Y").to_string(), "Fri Nov 28 12:00:09 2014");
    assert_eq!(dt.format_localized("%A %e %B %Y, %T", Locale::fr_BE).to_string(), "vendredi 28 novembre 2014, 12:00:09");
    assert_eq!(dt.format("%a %b %e %T %Y").to_string(), dt.format("%c").to_string());

    assert_eq!(dt.to_string(), "2014-11-28 12:00:09 UTC");
    assert_eq!(dt.to_rfc2822(), "Fri, 28 Nov 2014 12:00:09 +0000");
    assert_eq!(dt.to_rfc3339(), "2014-11-28T12:00:09+00:00");
    assert_eq!(format!("{:?}", dt), "2014-11-28T12:00:09Z");

    // Note that milli/nanoseconds are only printed if they are non-zero
    let dt_nano = Utc.ymd(2014, 11, 28).and_hms_nano(12, 0, 9, 1);
    assert_eq!(format!("{:?}", dt_nano), "2014-11-28T12:00:09.000000001Z");

Parsing can be done with three methods:

1. The standard `FromStr` trait (and `parse` method on a string) can be used for parsing `DateTime<FixedOffset>`, `DateTime<Utc>` and `DateTime<Local>` values. This parses what the `{:?}` (`std::fmt::Debug`) format specifier prints, and requires the offset to be present.

2. `DateTime::parse_from_str` parses a date and time with offsets and returns `DateTime<FixedOffset>`. This should be used when the offset is a part of input and the caller cannot guess that. It cannot be used when the offset can be missing. `DateTime::parse_from_rfc2822` and `DateTime::parse_from_rfc3339` are similar but for well-known formats.

3. `Offset::datetime_from_str` is similar but returns `DateTime` of given offset. When the explicit offset is missing from the input, it simply uses given offset. It issues an error when the input contains an explicit offset different from the current offset.

More detailed control over the parsing process is available via `format` module.

    use chrono::prelude::*;

    let dt = Utc.ymd(2014, 11, 28).and_hms(12, 0, 9);
    let fixed_dt = dt.with_timezone(&FixedOffset::east(9*3600));

    // method 1
    assert_eq!("2014-11-28T12:00:09Z".parse::<DateTime<Utc>>(), Ok(dt.clone()));
    assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<Utc>>(), Ok(dt.clone()));
    assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<FixedOffset>>(), Ok(fixed_dt.clone()));

    // method 2
    assert_eq!(DateTime::parse_from_str("2014-11-28 21:00:09 +09:00", "%Y-%m-%d %H:%M:%S %z"),
               Ok(fixed_dt.clone()));
    assert_eq!(DateTime::parse_from_rfc2822("Fri, 28 Nov 2014 21:00:09 +0900"),
               Ok(fixed_dt.clone()));
    assert_eq!(DateTime::parse_from_rfc3339("2014-11-28T21:00:09+09:00"), Ok(fixed_dt.clone()));

    // method 3
    assert_eq!(Utc.datetime_from_str("2014-11-28 12:00:09", "%Y-%m-%d %H:%M:%S"), Ok(dt.clone()));
    assert_eq!(Utc.datetime_from_str("Fri Nov 28 12:00:09 2014", "%a %b %e %T %Y"), Ok(dt.clone()));

    // oops, the year is missing!
    assert!(Utc.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T %Y").is_err());
    // oops, the format string does not include the year at all!
    assert!(Utc.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T").is_err());
    // oops, the weekday is incorrect!
    assert!(Utc.datetime_from_str("Sat Nov 28 12:00:09 2014", "%a %b %e %T %Y").is_err());

Again : See `format::strftime` documentation for full syntax and list of specifiers.

### Conversion from and to EPOCH timestamps

Use `Utc.timestamp(seconds, nanoseconds)` to construct a `DateTime<Utc>` from a UNIX timestamp (seconds, nanoseconds that passed since January 1st 1970).

Use `DateTime.timestamp` to get the timestamp (in seconds) from a `DateTime`. Additionally, you can use `DateTime.timestamp_subsec_nanos` to get the number of additional number of nanoseconds.

    // We need the trait in scope to use Utc::timestamp().
    use chrono::{DateTime, TimeZone, Utc};

    // Construct a datetime from epoch:
    let dt = Utc.timestamp(1_500_000_000, 0);
    assert_eq!(dt.to_rfc2822(), "Fri, 14 Jul 2017 02:40:00 +0000");

    // Get epoch value from a datetime:
    let dt = DateTime::parse_from_rfc2822("Fri, 14 Jul 2017 02:40:00 +0000").unwrap();
    assert_eq!(dt.timestamp(), 1_500_000_000);

### Individual date

Chrono also provides an individual date type (`Date`). It also has time zones attached, and have to be constructed via time zones. Most operations available to `DateTime` are also available to `Date` whenever appropriate.

    use chrono::prelude::*;
    use chrono::offset::LocalResult;

    assert_eq!(Utc::today(), Utc::now().date());
    assert_eq!(Local::today(), Local::now().date());

    assert_eq!(Utc.ymd(2014, 11, 28).weekday(), Weekday::Fri);
    assert_eq!(Utc.ymd_opt(2014, 11, 31), LocalResult::None);
    assert_eq!(Utc.ymd(2014, 11, 28).and_hms_milli(7, 8, 9, 10).format("%H%M%S").to_string(),
               "070809");

There is no timezone-aware `Time` due to the lack of usefulness and also the complexity.

`DateTime` has `date` method which returns a `Date` which represents its date component. There is also a `time` method, which simply returns a naive local time described below.

### Naive date and time

Chrono provides naive counterparts to `Date`, (non-existent) `Time` and `DateTime` as `NaiveDate`, `NaiveTime` and `NaiveDateTime` respectively.

They have almost equivalent interfaces as their timezone-aware twins, but are not associated to time zones obviously and can be quite low-level. They are mostly useful for building blocks for higher-level types.

Timezone-aware `DateTime` and `Date` types have two methods returning naive versions: `naive_local` returns a view to the naive local time, and `naive_utc` returns a view to the naive UTC time.

## Limitations

Only proleptic Gregorian calendar (i.e. extended to support older dates) is supported. Be very careful if you really have to deal with pre-20C dates, they can be in Julian or others.

Date types are limited in about +/- 262,000 years from the common epoch. Time types are limited in the nanosecond accuracy.

Leap seconds are supported in the representation but Chrono doesn’t try to make use of them. (The main reason is that leap seconds are not really predictable.) Almost every operation over the possible leap seconds will ignore them. Consider using `NaiveDateTime` with the implicit TAI (International Atomic Time) scale if you want.

Chrono inherently does not support an inaccurate or partial date and time representation. Any operation that can be ambiguous will return `None` in such cases. For example, “a month later” of 2014-01-30 is not well-defined and consequently `Utc.ymd(2014, 1, 30).with_month(2)` returns `None`.

Non ISO week handling is not yet supported. For now you can use the chrono_ext crate (sources).

Advanced time zone handling is not yet supported. For now you can try the Chrono-tz crate instead.

## Re-exports

`pub use format::ParseError;`
`pub use format::ParseResult;`
`pub use naive::IsoWeek;`
`pub use naive::NaiveDate;`
`pub use naive::NaiveDateTime;`
`pub use naive::NaiveTime;`
`pub use offset::Local;`
`pub use offset::FixedOffset;`
`pub use offset::LocalResult;`
`pub use offset::Offset;`
`pub use offset::TimeZone;`
`pub use offset::Utc;`

## Modules

format | Formatting (and parsing) utilities for date and time.
naive | Date and time types unconcerned with timezones.
offset | The time zone, which calculates offsets from the local time to UTC.
prelude | A convenience module appropriate for glob imports (`use chrono::prelude::*;`).

## Structs

Date | ISO 8601 calendar date with time zone.
DateTime | ISO 8601 combined date and time with time zone.
Duration | ISO 8601 time duration with nanosecond precision. This also allows for the negative duration; see individual methods for details.
ParseMonthError | An error resulting from reading `<Month>` value with `FromStr`.
ParseWeekdayError | An error resulting from reading `Weekday` value with `FromStr`.

## Enums

Month | The month of the year.
RoundingError | An error from rounding by `Duration`
SecondsFormat | Specific formatting options for seconds. This may be extended in the future, so exhaustive matching in external code is not recommended.
Weekday | The day of week.

## Constants

MAX_DATE | The maximum possible `Date`.
MAX_DATETIME | The maximum possible `DateTime<Utc>`.
MIN_DATE | The minimum possible `Date`.
MIN_DATETIME | The minimum possible `DateTime<Utc>`.

## Traits

Datelike | The common set of methods for date component.
DurationRound | Extension trait for rounding or truncating a DateTime by a Duration.
SubsecRound | Extension trait for subsecond rounding or truncation to a maximum number of digits. Rounding can be used to decrease the error variance when serializing/persisting to lower precision. Truncation is the default behavior in Chrono display formatting. Either can be used to guarantee equality (e.g. for testing) when round-tripping through a lower precision format.
Timelike | The common set of methods for time component.