Analysis of the Stack/Heap layout of a simple Vec<String> object.

rust_heap_analysis.rs

use std::mem;

fn print_mem_bytes(ptr: *const u8, limit: usize) {
    for i in 0..limit as isize {
        print!("{:02x} ", unsafe { *ptr.offset(i) });
    }
    println!();
}

fn main() {
    // Stack:
    //  - Vector { capacity, ptr_to_first_element, length }
    // Heap:
    //  - String { capacity, ptr_to_str, length }
    //  - str {"hello"}

    let mut arr: Vec<String> = Vec::with_capacity(0xEE);
    arr.push("hello".to_owned());

    let arr_ptr: *const u8 = &arr as *const _ as *const u8;
    let string0_ptr: *const u8 = &arr[0] as *const _ as *const u8;
    let str0_ptr: *const u8 = arr[0].as_str() as *const _ as *const u8;

    print!("\nVector data at ${arr_ptr:018p} (Stack):\n\n\t");
    print_mem_bytes(arr_ptr, mem::size_of_val(&arr));

    print!("\nVector[0] data at ${string0_ptr:018p} (Heap):\n\n\t");
    print_mem_bytes(string0_ptr, mem::size_of_val(&arr[0]));

    print!("\nVector[0]'s &str data at ${str0_ptr:018p} (Heap):\n\n\t");
    print_mem_bytes(str0_ptr, mem::size_of_val(arr[0].as_str()));

    // Output:
    //
    // Vector data at $0x0000009435fff170 (Stack):
    //
    //     _______________________________________________________________________
    //    |      arr.capacity     |   pointer to arr[0]   |      arr.length       |
    //     ee 00 00 00 00 00 00 00 a0 7e 43 dd 3a 02 00 00 01 00 00 00 00 00 00 00
    //
    //
    // Vector[0] data at $0x0000023add437ea0 (Heap):
    //
    //     _______________________________________________________________________
    //    |    arr[0].capacity    |  ptr to arr[0]'s str  |     arr[0].length     |
    //     05 00 00 00 00 00 00 00 20 4e 42 dd 3a 02 00 00 05 00 00 00 00 00 00 00
    //
    //
    // Vector[0]'s &str data at $0x0000023add424e20 (Heap):
    //
    //     ______________
    //    |h  e  l  l  o |
    //     68 65 6c 6c 6f
}