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Puzzle 11: Explanation

Explore how Rust handles memory allocation using the stack and the heap in this lesson. Understand why large data structures can cause stack overflow, how Box and Vec types manage heap storage differently, and how compiler optimizations influence memory usage. Learn practical solutions for safely storing large arrays and the implications of using unstable Rust features for memory management.

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Test it out

Hit “Run” to see the code’s output. The answer depends on how we run the program.

Debug mode

Pressing “Run” will cause the program to crash and display an error message:

C++
fn main() {
    let c = Box::new([0u32; 10_000_000]);
    println!("{}", c.len());
}

Release mode

Pressing “Run” in release mode will display the following output:

10000000

[package]
name = "boxes"
version = "0.1.0"
authors = ["Herbert Wolverson <herberticus@gmail.com>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
Running in release mode

Explanation

10,000,00010,000,000 3232-bit integers require 4040 ...