# Struct std::time::SystemTime [−] [src]

    pub struct SystemTime(_);

Unstable (`time2` #29866)

: recently added

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 second. 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.

## Methods

### `impl SystemTime`

#### `fn now() -> SystemTime`

Unstable (`time2` #29866)

: recently added

Returns the system time corresponding to "now".

#### `fn duration_from_earlier(&self, earlier: SystemTime) -> Result<Duration, SystemTimeError>`

Unstable (`time2` #29866)

: recently added

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).

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.

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

Unstable (`time2` #29866)

: recently added

Returns the amount of time elapsed since this system time was created.

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 may 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.

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.

## Trait Implementations

### `impl Add<Duration> for SystemTime`

#### `type Output = SystemTime`

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

### `impl Sub<Duration> for SystemTime`

#### `type Output = SystemTime`

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

### `impl Debug for SystemTime`

#### `fn fmt(&self, f: &mut Formatter) -> Result`

### Derived Implementations

### `impl Ord for SystemTime`

#### `fn cmp(&self, __arg_0: &SystemTime) -> Ordering`

### `impl PartialOrd for SystemTime`

#### `fn partial_cmp(&self, __arg_0: &SystemTime) -> Option<Ordering>`

#### `fn lt(&self, __arg_0: &SystemTime) -> bool`

#### `fn le(&self, __arg_0: &SystemTime) -> bool`

#### `fn gt(&self, __arg_0: &SystemTime) -> bool`

#### `fn ge(&self, __arg_0: &SystemTime) -> bool`

### `impl Eq for SystemTime`

### `impl PartialEq for SystemTime`

#### `fn eq(&self, __arg_0: &SystemTime) -> bool`

#### `fn ne(&self, __arg_0: &SystemTime) -> bool`

### `impl Clone for SystemTime`

#### `fn clone(&self) -> SystemTime`

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

### `impl Copy for SystemTime`

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