Crate std

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<T> and Option<T>, 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:

1. 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.
2. 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<T> 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.

Contributing changes to the documentation

Check out the rust contribution guidelines here. The source for this documentation can be found on Github. To contribute changes, make sure you read the guidelines first, then submit pull-requests for your suggested changes.

Contributions are appreciated! If you see a part of the docs that can be improved, submit a PR, or chat with us first on irc.mozilla.org #rust-docs.

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<T> and Result<T, E>. The iter module defines Rust's iterator trait, Iterator, which works with the for loop to access collections.

The standard library exposes three 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 flavors 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 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<K, V>.

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 character type.
f32	The 32-bit floating point type.
f64	The 64-bit floating point type.
fn	Function pointers, like fn(usize) -> bool.
i8	The 8-bit signed integer type.
i16	The 16-bit signed integer type.
i32	The 32-bit signed integer type.
i64	The 64-bit signed integer type.
isize	The pointer-sized signed integer type.
pointer	Raw, unsafe pointers, *const T, and *mut T.
reference	References, both shared and mutable.
slice	A dynamically-sized view into a contiguous sequence, [T].
str	String slices.
tuple	A finite heterogeneous sequence, (T, U, ..).
u8	The 8-bit unsigned integer type.
u16	The 16-bit unsigned integer type.
u32	The 32-bit unsigned integer type.
u64	The 64-bit unsigned integer type.
unit	The () type, sometimes called "unit" or "nil".
usize	The pointer-sized unsigned integer type.
i128	[ Experimental ] The 128-bit signed integer type.
never	[ Experimental ] The ! type, also called "never".
u128	[ Experimental ] The 128-bit unsigned 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 character type.
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	This module provides constants which are specific to the implementation of the f32 floating point data type.
f64	This module provides constants which are specific to the implementation of the f64 floating point data type.
ffi	Utilities related to FFI bindings.
fmt	Utilities for formatting and printing Strings.
fs	Filesystem manipulation operations.
hash	Generic hashing support.
i8	The 8-bit signed integer type.
i16	The 16-bit signed integer type.
i32	The 32-bit signed integer type.
i64	The 64-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 iteration.
marker	Primitive traits and types representing basic properties of types.
mem	Basic functions for dealing with memory.
net	Networking primitives for TCP/UDP communication.
num	Additional functionality for numerics.
ops	Overloadable operators.
option	Optional values.
os	OS-specific functionality.
panic	Panic support in the standard library.
path	Cross-platform path manipulation.
prelude	The Rust Prelude.
process	A module for working with processes.
ptr	Raw, unsafe pointers, *const T, and *mut T.
rc	Single-threaded reference-counting pointers. 'Rc' stands for 'Reference Counted'.
result	Error handling with the Result type.
slice	A dynamically-sized view into a contiguous sequence, [T].
str	Unicode string slices.
string	A UTF-8 encoded, growable string.
sync	Useful synchronization primitives.
thread	Native threads.
time	Temporal quantification.
u8	The 8-bit unsigned integer type.
u16	The 16-bit unsigned integer type.
u32	The 32-bit unsigned integer type.
u64	The 64-bit unsigned integer type.
usize	The pointer-sized unsigned integer type.
vec	A contiguous growable array type with heap-allocated contents, written Vec<T>.
heap	[ Experimental ] dox
i128	[ Experimental ] The 128-bit signed integer type.
intrinsics	[ Experimental ] rustc compiler intrinsics.
raw	[ Experimental ] Contains struct definitions for the layout of compiler built-in types.
u128	[ Experimental ] The 128-bit unsigned integer type.

Macros

assert	Ensure that a boolean expression is true at runtime.
assert_eq	Asserts that two expressions are equal to each other (using PartialEq).
assert_ne	Asserts that two expressions are not equal to each other (using PartialEq).
cfg	Boolean evaluation of configuration flags, at compile-time.
column	A macro which expands to the column number on which it was invoked.
compile_error	Unconditionally causes compilation to fail with the given error message when encountered.
concat	Concatenates literals into a static string slice.
debug_assert	Ensure that a boolean expression is true at runtime.
debug_assert_eq	Asserts that two expressions are equal to each other.
debug_assert_ne	Asserts that two expressions are not equal to each other.
env	Inspect an environment variable at compile time.
eprint	Macro for printing to the standard error.
eprintln	Macro for printing to the standard error, with a newline.
file	A macro which expands to the file name from which it was invoked.
format	Creates a String using interpolation of runtime expressions.
format_args	The core macro for formatted string creation & output.
include	Parse a file as an expression or an item according to the context.
include_bytes	Includes a file as a reference to a byte array.
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, with a newline.
stringify	A macro which stringifies its arguments.
thread_local	Declare a new thread local storage key of type std::thread::LocalKey.
concat_idents	[ Experimental ] Concatenate identifiers into one identifier.
select	[ Experimental ] A macro to select an event from a number of receivers.
try	Helper macro for reducing boilerplate code for matching Result together with converting downstream errors.
unimplemented	A standardized placeholder for marking unfinished code.
unreachable	A utility macro for indicating unreachable code.
vec	Creates a Vec containing the arguments.
write	Write formatted data into a buffer.
writeln	Write formatted data into a buffer, with a newline appended.

Traits

Termination

[ Experimental ] A trait for implementing arbitrary return types in the main function.