Module std::alloc

1.28.0 · source ·
Expand description

Memory allocation APIs.

In a given program, the standard library has one “global” memory allocator that is used for example by Box<T> and Vec<T>.

Currently the default global allocator is unspecified. Libraries, however, like cdylibs and staticlibs are guaranteed to use the System by default.

§The #[global_allocator] attribute

This attribute allows configuring the choice of global allocator. You can use this to implement a completely custom global allocator to route all default allocation requests to a custom object.

use std::alloc::{GlobalAlloc, System, Layout};

struct MyAllocator;

unsafe impl GlobalAlloc for MyAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout)

static GLOBAL: MyAllocator = MyAllocator;

fn main() {
    // This `Vec` will allocate memory through `GLOBAL` above
    let mut v = Vec::new();

The attribute is used on a static item whose type implements the GlobalAlloc trait. This type can be provided by an external library:

use jemallocator::Jemalloc;

static GLOBAL: Jemalloc = Jemalloc;

fn main() {}

The #[global_allocator] can only be used once in a crate or its recursive dependencies.


  • Layout of a block of memory.
  • The parameters given to Layout::from_size_align or some other Layout constructor do not satisfy its documented constraints.
  • The default memory allocator provided by the operating system.
  • AllocErrorExperimental
    The AllocError error indicates an allocation failure that may be due to resource exhaustion or to something wrong when combining the given input arguments with this allocator.
  • GlobalExperimental
    The global memory allocator.


  • A memory allocator that can be registered as the standard library’s default through the #[global_allocator] attribute.
  • AllocatorExperimental
    An implementation of Allocator can allocate, grow, shrink, and deallocate arbitrary blocks of data described via Layout.


  • Allocate memory with the global allocator.
  • Allocate zero-initialized memory with the global allocator.
  • Deallocate memory with the global allocator.
  • Signal a memory allocation error.
  • Reallocate memory with the global allocator.
  • Registers a custom allocation error hook, replacing any that was previously registered.
  • Unregisters the current allocation error hook, returning it.

Type Aliases§