pointersrustborrow

What do the '&&' and star '**' symbols mean in Rust?

fn main() {
    let c: i32 = 5;
    let rrc = &&c;
    println!("{}", rrc); // 5
    println!("{}", *rrc); // 5
    println!("{}", **rrc); // 5
}

In C/C++ language, rrc likes a two level pointer. In this example, rrc doesn't mean this in rust. What do & and * mean in Rust?

Solution

  • The reason they all print the same thing is that borrows (&T) in Rust implements Display for T: Display by dispatching it to the pointed type. If you want to print the actual pointer value, you have to use {:p}.

    let c = 5;
let rrc = &&c;
println!("{:p}", rrc); // 0x7ffc4e4c7590
println!("{:p}", *rrc); // 0x7ffc4e4c7584
println!("{}", **rrc); // 5

    See the playground.