Cargo Basics

Creating a New Project

cargo new scaffolds a complete, ready-to-build Rust project: it creates a project folder, a Cargo.toml manifest file, a src/ directory, and a starter src/main.rs file containing a 'Hello, world!' program.

Example: Creating a New Project

cargo new hello_cargo

The Cargo.toml Manifest

Cargo.toml is the project's manifest file. It records the package name, version, Rust edition, and any external dependencies (crates) the project needs. Cargo reads this file to know how to build your project.

Example: The Cargo.toml Manifest

[package]
name = "hello_cargo"
version = "0.1.0"
edition = "2021"

[dependencies]

The src Directory

Cargo expects your source code inside a src/ folder, with src/main.rs as the entry point for a binary program. Keeping this structure means every Cargo command knows exactly where to find your code without extra configuration.

Example: The src Directory

// Entry point: execution of the program starts here
fn main() {
    // Print "Generated by cargo new" to the console (with a trailing newline)
    println!("Generated by cargo new");
}

Why Use Cargo Instead of rustc Directly

As soon as a project grows beyond one file or needs external libraries, calling rustc directly becomes tedious.

Cargo automates compiling, dependency management, testing, and packaging with a handful of simple subcommands, which is why virtually all real Rust projects use it.

Example: Why Use Cargo Instead of rustc Directly

// Entry point: execution of the program starts here
fn main() {
    // Declare an immutable variable `reasons`, set to `["dependency management", "consistent builds", "built-in testing"]`
    let reasons = ["dependency management", "consistent builds", "built-in testing"];
    // Loop over `reasons.iter()`, binding each item to `r`
    for r in reasons.iter() {
        // Print "Cargo handles: {}" to the console, substituting in `r` (with a trailing newline)
        println!("Cargo handles: {}", r);
    }
}