Crate std [−] [src]

The Rust Standard Library

The Rust Standard Library is the foundation of portable Rust software, a set of minimal and battle-tested shared abstractions for the broader Rust ecosystem. It offers core types, like Vec and Option, library-defined operations on language primitives, standard macros, I/O and multithreading, among many other things.

std is available to all Rust crates by default, just as if each one contained an extern crate std import at the crate root. Therefore the standard library can be accessed in use statements through the path std, as in use std::env, or in expressions through the absolute path ::std, as in ::std::env::args().

How to read this documentation

If you already know the name of what you are looking for the fastest way to find it is to use the search bar at the top of the page.

Otherwise, you may want to jump to one of these useful sections:

std::* modules
Primitive types
Standard macros
The Rust Prelude

If this is your first time, the documentation for the standard library is written to be casually perused. Clicking on interesting things should generally lead you to interesting places. Still, there are important bits you don't want to miss, so read on for a tour of the standard library and its documentation!

Once you are familiar with the contents of the standard library you may begin to find the verbosity of the prose distracting. At this stage in your development you may want to press the [-] button near the top of the page to collapse it into a more skimmable view.

While you are looking at that [-] button also notice the [src] button. Rust's API documentation comes with the source code and you are encouraged to read it. The standard library source is generally high quality and a peek behind the curtains is often enlightening.

What is in the standard library documentation?

First of all, The Rust Standard Library is divided into a number of focused modules, all listed further down this page. These modules are the bedrock upon which all of Rust is forged, and they have mighty names like std::slice and std::cmp. Modules' documentation typically includes an overview of the module along with examples, and are a smart place to start familiarizing yourself with the library.

Second, implicit methods on primitive types are documented here. This can be a source of confusion for two reasons:

While primitives are implemented by the compiler, the standard library implements methods directly on the primitive types (and it is the only library that does so), which are documented in the section on primitives.
The standard library exports many modules with the same name as primitive types. These define additional items related to the primitive type, but not the all-important methods.

So for example there is a page for the primitive type i32 that lists all the methods that can be called on 32-bit integers (very useful), and there is a page for the module std::i32 that documents the constant values MIN and MAX (rarely useful).

Note the documentation for the primitives str and [T] (also called 'slice'). Many method calls on String and Vec are actually calls to methods on str and [T] respectively, via deref coercions.

Third, the standard library defines The Rust Prelude, a small collection of items - mostly traits - that are imported into every module of every crate. The traits in the prelude are pervasive, making the prelude documentation a good entry point to learning about the library.

And finally, the standard library exports a number of standard macros, and lists them on this page (technically, not all of the standard macros are defined by the standard library - some are defined by the compiler - but they are documented here the same). Like the prelude, the standard macros are imported by default into all crates.

A Tour of The Rust Standard Library

The rest of this crate documentation is dedicated to pointing out notable features of The Rust Standard Library.

Containers and collections

The option and result modules define optional and error-handling types, Option and Result. The iter module defines Rust's iterator trait, Iterator, which works with the for loop to access collections.

The standard library exposes 3 common ways to deal with contiguous regions of memory:

Vec<T> - A heap-allocated vector that is resizable at runtime.
[T; n] - An inline array with a fixed size at compile time.
[T] - A dynamically sized slice into any other kind of contiguous storage, whether heap-allocated or not.

Slices can only be handled through some kind of pointer, and as such come in many flavours such as:

&[T] - shared slice
&mut [T] - mutable slice
Box<[T]> - owned slice

str, a UTF-8 string slice, is a primitive type, and the standard library defines many methods for it. Rust strs are typically accessed as immutable references: &str. Use the owned String type defined in string for building and mutating strings.

For converting to strings use the format! macro, and for converting from strings use the FromStr trait.

Data may be shared by placing it in a reference-counted box or the Rc type, and if further contained in a Cell or RefCell, may be mutated as well as shared. Likewise, in a concurrent setting it is common to pair an atomically-reference-counted box, Arc, with a Mutex to get the same effect.

The collections module defines maps, sets, linked lists and other typical collection types, including the common HashMap.

Platform abstractions and I/O

Besides basic data types, the standard library is largely concerned with abstracting over differences in common platforms, most notably Windows and Unix derivatives.

Common types of I/O, including files, TCP, UDP, are defined in the io, fs, and net modules.

The thread module contains Rust's threading abstractions. sync contains further primitive shared memory types, including atomic and mpsc, which contains the channel types for message passing.

Primitive Types

array	A fixed-size array, denoted `[T; N]`, for the element type, `T`, and the non-negative compile time constant size, `N`.
bool	The boolean type.
char	A Unicode scalar value.
f32	The 32-bit floating point type.
f64	The 64-bit floating point type.
i16	The 16-bit signed integer type.
i32	The 32-bit signed integer type.
i64	The 64-bit signed integer type.
i8	The 8-bit signed integer type.
isize	The pointer-sized signed integer type.
pointer	Raw, unsafe pointers, `const T`, and `mut T`.
slice	A dynamically-sized view into a contiguous sequence, `[T]`.
str	Unicode string slices.
tuple	A finite heterogeneous sequence, `(T, U, ..)`.
u16	The 16-bit unsigned integer type.
u32	The 32-bit unsigned integer type.
u64	The 64-bit unsigned integer type.
u8	The 8-bit unsigned integer type.
usize	The pointer-sized signed integer type.

Modules

any	This module implements the `Any` trait, which enables dynamic typing of any `'static` type through runtime reflection.
ascii	Operations on ASCII strings and characters
borrow	A module for working with borrowed data.
boxed	A pointer type for heap allocation.
cell	Shareable mutable containers.
char	A Unicode scalar value
clone	The `Clone` trait for types that cannot be 'implicitly copied'
cmp	Functionality for ordering and comparison.
collections	Collection types.
convert	Traits for conversions between types.
default	The `Default` trait for types which may have meaningful default values.
env	Inspection and manipulation of the process's environment.
error	Traits for working with Errors.
f32	The 32-bit floating point type.
f64	The 64-bit floating point type.
ffi	Utilities related to FFI bindings.
fmt	Utilities for formatting and printing strings
fs	Filesystem manipulation operations
hash	Generic hashing support.
i16	The 16-bit signed integer type.
i32	The 32-bit signed integer type.
i64	The 64-bit signed integer type.
i8	The 8-bit signed integer type.
io	Traits, helpers, and type definitions for core I/O functionality.
isize	The pointer-sized signed integer type.
iter	Composable external iterators
marker	Primitive traits and marker types representing basic 'kinds' of types.
mem	Basic functions for dealing with memory
net	Networking primitives for TCP/UDP communication.
num	Numeric traits and functions for generic mathematics
ops	Overloadable operators
option	Optional values
os	OS-specific functionality
path	Cross-platform path manipulation.
prelude	The Rust Prelude
process	Working with processes.
ptr	Raw, unsafe pointers, `const T`, and `mut T`
rc	Thread-local reference-counted boxes (the `Rc<T>` type).
result	Error handling with the `Result` type
slice	A dynamically-sized view into a contiguous sequence, `[T]`.
str	Unicode string slices
string	An owned, growable string that enforces that its contents are valid UTF-8.
sync	Useful synchronization primitives
thread	Native threads
time	Temporal quantification.
u16	The 16-bit unsigned integer type.
u32	The 32-bit unsigned integer type.
u64	The 64-bit unsigned integer type.
u8	The 8-bit unsigned integer type.
usize	The pointer-sized unsigned integer type.
vec	A growable list type with heap-allocated contents, written `Vec<T>` but pronounced 'vector.'
dynamic_lib	[Unstable] Dynamic library facilities.
intrinsics	[Unstable] rustc compiler intrinsics.
raw	[Unstable] Contains struct definitions for the layout of compiler built-in types.
rt	[Unstable] Runtime services
simd	[Unstable] SIMD vectors.

Macros

assert!	Ensure that a boolean expression is `true` at runtime.
assert_eq!	Asserts that two expressions are equal to each other.
cfg!	Boolean evaluation of configuration flags.
column!	A macro which expands to the column number on which it was invoked.
concat!	Concatenates literals into a static string slice.
concat_idents!	Concatenate identifiers into one identifier.
debug_assert!	Ensure that a boolean expression is `true` at runtime.
debug_assert_eq!	Asserts that two expressions are equal to each other, testing equality in both directions.
env!	Inspect an environment variable at compile time.
file!	A macro which expands to the file name from which it was invoked.
format!	Use the syntax described in `std::fmt` to create a value of type `String`. See `std::fmt` for more information.
format_args!	The core macro for formatted string creation & output.
include!	Parse the current given file as an expression.
include_bytes!	Includes a file as a byte slice.
include_str!	Includes a utf8-encoded file as a string.
line!	A macro which expands to the line number on which it was invoked.
module_path!	Expands to a string that represents the current module path.
option_env!	Optionally inspect an environment variable at compile time.
panic!	The entry point for panic of Rust threads.
print!	Macro for printing to the standard output.
println!	Macro for printing to the standard output.
scoped_thread_local!	Declare a new scoped thread local storage key.
select!	A macro to select an event from a number of receivers.
stringify!	A macro which stringifies its argument.
thread_local!	Declare a new thread local storage key of type `std::thread::LocalKey`.
try!	Helper macro for unwrapping `Result` values while returning early with an error if the value of the expression is `Err`. Can only be used in functions that return `Result` because of the early return of `Err` that it provides.
unimplemented!	A standardised placeholder for marking unfinished code. It panics with the message `"not yet implemented"` when executed.
unreachable!	A utility macro for indicating unreachable code.
vec!	Creates a `Vec` containing the arguments.
write!	Use the `format!` syntax to write data into a buffer of type `&mut Write`. See `std::fmt` for more information.
writeln!	Equivalent to the `write!` macro, except that a newline is appended after the message is written.