Pointers

Terms

  • value: combination of a type and relevant element
  • variable: named value slot on the stack
  • place: can hold a value somewhere in memory, either on the stack, heap, registers or disk
  • pointer: a value holding an address to a place

Example

This example is to show that a pointer has a value with an address that it's pointing to, but it also has it's own address.

Create two pointers to i32 and print the pointers, Rust will automatically dereference them:


#![allow(unused)]
fn main() {
let x = 10;
let y = 20;

let mut x_pointer = &x;
let y_pointer = &y;

println!("\nx_pointer dereferenced: {x_pointer}\ny_pointer dereferenced: {y_pointer}");
}
x_pointer dereferenced: 10
y_pointer dereferenced: 20

Print out the address that's inside the pointer using the :p format specifier:


#![allow(unused)]
fn main() {
println!("\nx address: {x_pointer:p}\ny address: {y_pointer:p}");
}
x address: 0x7ffd532910e0
y address: 0x7ffd532910e4

Print the address of the pointer value itself by creating a pointer to the pointer with & and printing it with :p:


#![allow(unused)]
fn main() {
println!("\nx_pointer address: {:p}\ny_pointer address: {:p}", &x_pointer, &y_pointer);
}
x_pointer address: 0x7fffba86ec48
y_pointer address: 0x7fffba86ec50

Change the address that x_pointer is pointing to and dereference it


#![allow(unused)]
fn main() {
x_pointer = y_pointer;
println!("\nx_pointer dereferenced: {}", x_pointer);
}
x_pointer dereferenced: 20

x_pointer and y_pointer now point to the same address known as a shared_reference