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. Therefore, the standard library can be accessed in use statements through the path std, as in use std::env.

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 Discord #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.

Re-exports

pub use core::arch;

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	A 32-bit floating point type (specifically, the "binary32" type defined in IEEE 754-2008).
f64	A 64-bit floating point type (specifically, the "binary64" type defined in IEEE 754-2008).
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.
i128	The 128-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]. Contiguous here means that elements are laid out so that every element is the same distance from its neighbors.
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.
u128	The 128-bit unsigned integer type.
unit	The () type, also called "unit".
usize	The pointer-sized unsigned integer type.
never	Experimental The ! type, also called "never".

Modules

alloc	Memory allocation APIs
any
array
ascii	Operations on ASCII strings and characters.
borrow
boxed
cell
char
clone
cmp
collections	Collection types.
convert
default
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
fs	Filesystem manipulation operations.
future	Asynchronous values.
hash
hint
i8
i16
i32
i64
i128
io	Traits, helpers, and type definitions for core I/O functionality.
isize
iter
marker
mem
net	Networking primitives for TCP/UDP communication.
num	Additional functionality for numerics.
ops
option
os	OS-specific functionality.
panic	Panic support in the standard library.
path	Cross-platform path manipulation.
pin
prelude	The Rust Prelude.
primitive
process	A module for working with processes.
ptr
rc
result
slice
str
string
sync	Useful synchronization primitives.
task	Types and Traits for working with asynchronous tasks.
thread	Native threads.
time	Temporal quantification.
u8
u16
u32
u64
u128
usize
vec
backtrace	Experimental Support for capturing a stack backtrace of an OS thread
intrinsics	Experimental
lazy	Experimental Lazy values and one-time initialization of static data.
raw	Experimental

Macros

assert
assert_eq
assert_ne
cfg
column
compile_error
concat
dbg	Prints and returns the value of a given expression for quick and dirty debugging.
debug_assert
debug_assert_eq
debug_assert_ne
env
eprint	Prints to the standard error.
eprintln	Prints to the standard error, with a newline.
file
format
format_args
include
include_bytes
include_str
is_x86_feature_detected	A macro to test at runtime whether a CPU feature is available on x86/x86-64 platforms.
line
matches
module_path
option_env
panic	Panics the current thread.
print	Prints to the standard output.
println	Prints to the standard output, with a newline.
stringify
thread_local	Declare a new thread local storage key of type std::thread::LocalKey.
todo
try	Deprecated
unimplemented
unreachable
vec
write
writeln
asm	Experimental
concat_idents	Experimental
format_args_nl	Experimental
global_asm	Experimental
is_aarch64_feature_detected	Experimental Prevents compilation if is_aarch64_feature_detected is used somewhere else than aarch64 targets.
is_arm_feature_detected	Experimental Prevents compilation if is_arm_feature_detected is used somewhere else than ARM targets.
is_mips64_feature_detected	Experimental Prevents compilation if is_mips64_feature_detected is used somewhere else than MIPS64 targets.
is_mips_feature_detected	Experimental Prevents compilation if is_mips_feature_detected is used somewhere else than MIPS targets.
is_powerpc64_feature_detected	Experimental Prevents compilation if is_powerpc64_feature_detected is used somewhere else than PowerPC64 targets.
is_powerpc_feature_detected	Experimental Prevents compilation if is_powerpc_feature_detected is used somewhere else than PowerPC targets.
llvm_asm	Experimental
log_syntax	Experimental
trace_macros	Experimental

Keywords

Self	The implementing type within a trait or impl block, or the current type within a type definition.
as	Cast between types, or rename an import.
async	Return a Future instead of blocking the current thread.
await	Suspend execution until the result of a Future is ready.
break	Exit early from a loop.
const	Compile-time constants and deterministic functions.
continue	Skip to the next iteration of a loop.
crate	A Rust binary or library.
dyn	dyn is a prefix of a trait object's type.
else	What expression to evaluate when an if condition evaluates to false.
enum	A type that can be any one of several variants.
extern	Link to or import external code.
false	A value of type bool representing logical false.
fn	A function or function pointer.
for	Iteration with in, trait implementation with impl, or higher-ranked trait bounds (for<'a>).
if	Evaluate a block if a condition holds.
impl	Implement some functionality for a type.
in	Iterate over a series of values with for.
let	Bind a value to a variable.
loop	Loop indefinitely.
match	Control flow based on pattern matching.
mod	Organize code into modules.
move	Capture a closure's environment by value.
mut	A mutable variable, reference, or pointer.
pub	Make an item visible to others.
ref	Bind by reference during pattern matching.
return	Return a value from a function.
self	The receiver of a method, or the current module.
static	A static item is a value which is valid for the entire duration of your program (a 'static lifetime).
struct	A type that is composed of other types.
super	The parent of the current module.
trait	A common interface for a group of types.
true	A value of type bool representing logical true.
type	Define an alias for an existing type.
union	The Rust equivalent of a C-style union.
unsafe	Code or interfaces whose memory safety cannot be verified by the type system.
use	Import or rename items from other crates or modules.
where	Add constraints that must be upheld to use an item.
while	Loop while a condition is upheld.