Rust manual memory management

Question

When I began learning C, I implemented common data structures such as lists, maps and trees. I used malloc, calloc, realloc and free to manage the memory manually when requested. I did the same thing with C++, using new and delete.

Now comes Rust. It seems like Rust doesn't offer any functions or operators which correspond to the ones of C or C++, at least in the stable release.

Are the Heap structure and the ptr module (marked with experimental) the ones to look at for this kind of thing?

I know that these data structures are already in the language. It's for the sake of learning.

Answer 1

Although it's really not recommended to do this ever, you can use malloc and free like you are used to from C. It's not very useful, but here's how it looks:

extern crate libc; // 0.2.65

use std::mem;

fn main() {
    unsafe {
        let my_num: *mut i32 = libc::malloc(mem::size_of::<i32>() as libc::size_t) as *mut i32;
        if my_num.is_null() {
            panic!("failed to allocate memory");
        }
        libc::free(my_num as *mut libc::c_void);
    }
}

A better approach is to use Rust's standard library:

use std::alloc::{alloc, dealloc, Layout};

fn main() {
    unsafe {
        let layout = Layout::new::<u16>();
        let ptr = alloc(layout);

        *(ptr as *mut u16) = 42;
        assert_eq!(*(ptr as *mut u16), 42);

        dealloc(ptr, layout);
    }
}