alloc crate

Use the heap with the alloc crate.

The alloc crate

If there's a memory allocator, no_std code can use the alloc crate to reach Vec, String, Box, Rc, BTreeMap and format!:

#![no_std]
extern crate alloc;

use alloc::string::String;
use alloc::vec::Vec;
use alloc::format;

pub fn rapor(v: &[u32]) -> String {
    let ciftler: Vec<u32> = v.iter().copied().filter(|x| x % 2 == 0).collect();
    format!("{} çift", ciftler.len())
}

The application provides the allocator: on embedded systems a crate like embedded-alloc is registered with #[global_allocator].

alloc within std

The alloc crate can be used explicitly in normal programs too; it's a way to show the code is ready to move to no_std:

extern crate alloc;

use alloc::string::String;
use alloc::vec::Vec;

let mut v: Vec<i32> = Vec::new();
v.push(1);
let s = String::from("merhaba");

std::vec::Vec and alloc::vec::Vec are the same type; only the path differs.

Exercise alloc types

Write extern crate alloc; and use alloc::vec::Vec and alloc::string::String. Create a vector holding 1 and 2 and the text "merhaba", and print both separated by a space (the vector with {:?}).

Show example solution

extern crate alloc;

use alloc::string::String;
use alloc::vec::Vec;

fn main() {
    let mut v: Vec<i32> = Vec::new();
    v.push(1);
    v.push(2);
    let s = String::from("merhaba");
    println!("{:?} {}", v, s);
}

Test yourself

Why is <code>HashMap</code> not in alloc while <code>BTreeMap</code> is?
- Both are there
- HashMap's default hasher needs a random seed from the OS
- HashMap is slower
- BTreeMap is newer
Show answer

HashMap's default hasher needs a random seed from the OS — In a no_std environment, the hashbrown crate provides a HashMap with your own hash function.

Allocation crate

extern crate ____;
use alloc::vec::Vec;

Show answer

extern crate alloc;
use alloc::vec::Vec;

Path and type

alloc::vec::Vec

Dynamic array
alloc::string::String

Owned text
alloc::boxed::Box

Heap box
alloc::collections::BTreeMap

Sorted map

Next lesson: Embedded

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies