Your first Rust program

In this section, you will learn how to create and compile your first Rust program using tools such as cargo.

Anatomy of a Rust program

A basic Rust program is organized as follows:

Cargo.toml
Cargo.lock
src
└── main.rs
target
└── debug
    └── myprogram

• The file Cargo.toml describes your program (name, version, authors, …).
• The file Cargo.lock contains information about the version of the other packages used when compiling your program.
• src contains the source of your program — main.rs is the file containing the main function.
• target is a directory created by the compiler; it will contain the output of the compilation, including the executable produced from your source files, in debug/myprogram (if myprogram is the name of your program as described in Cargo.toml). The target directory should never be checked in your version control software. It should be ignored completely (e.g., by adding it to your .gitignore if you are using git).

Creating your first Rust program: intro

Exercise 0.a: Create the skeleton of your first Rust program by using the command cargo new:

$ cargo new intro
     Created binary (application) `intro` package

This will create a intro directory with a complete skeleton of a Rust program:

$ tree intro
intro
├── Cargo.toml
└── src
    └── main.rs

(you might not have the tree on your computer – never mind, we will not need it)

Change your current directory to intro and display the content of main.rs:

$ cd intro
$ cat src/main.rs
fn main() {
    println!("Hello, world!");
}

As you can see, the program is pretty basic. You can compile it by using cargo build:

$ cargo build
   Compiling intro v0.1.0 (/tmp/intro)
    Finished dev [unoptimized + debuginfo] target(s) in 0.54s

Your program has compiled without errors. You can execute it by using cargo run:

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/intro`
Hello, world!

Note that you can execute cargo run without first executing cargo build: the application will be built automatically.

Editing the Rust program

Exercise 0.b: Using your editor of choice (for example Lapce, Emacs, Neovim, or Visual Studio code), edit main.rs so that the main program now displays a count from 1 to 5 inclusive:

fn main() {
    for i in 1..=5 {
        println!("i = {i}");
    }
}

Ensure that your editor is Rust-aware, or install the necessary extensions if needed. For Visual Studio Code, we suggest the installation of the "rust-analyzer" extension.

You can now execute your code. If everything went well, you should see the following output:

$ cargo run
   Compiling intro v0.1.0 (/tmp/intro)
    Finished dev [unoptimized + debuginfo] target(s) in 0.20s
     Running `target/debug/intro`
i = 1
i = 2
i = 3
i = 4
i = 5

You can also compile your program and run the executable directly. As cargo run output indicates it is located in target/debug/intro:

$ cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 0.00s
$ ls -l target/debug/intro
-rwxr-xr-x 2 sam sam 4203904 Jan 16 15:02 target/debug/intro
$ target/debug/intro
i = 1
i = 2
i = 3
i = 4
i = 5