Creating a New Package
To start a new package with Cargo, use cargo new
:
$ cargo new hello_world --bin
We’re passing --bin
because we’re making a binary program: if we
were making a library, we’d pass --lib
. This also initializes a new git
repository by default. If you don't want it to do that, pass --vcs none
.
Let’s check out what Cargo has generated for us:
$ cd hello_world
$ tree .
.
├── Cargo.toml
└── src
└── main.rs
1 directory, 2 files
Let’s take a closer look at Cargo.toml
:
[package]
name = "hello_world"
version = "0.1.0"
authors = ["Your Name <you@example.com>"]
edition = "2018"
[dependencies]
This is called a manifest, and it contains all of the metadata that Cargo needs to compile your package.
Here’s what’s in src/main.rs
:
fn main() { println!("Hello, world!"); }
Cargo generated a “hello world” for us. Let’s compile it:
$ cargo build
Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)
And then run it:
$ ./target/debug/hello_world
Hello, world!
We can also use cargo run
to compile and then run it, all in one step (You
won't see the Compiling
line if you have not made any changes since you last
compiled):
$ cargo run
Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)
Running `target/debug/hello_world`
Hello, world!
You’ll now notice a new file, Cargo.lock
. It contains information about our
dependencies. Since we don’t have any yet, it’s not very interesting.
Once you’re ready for release, you can use cargo build --release
to compile
your files with optimizations turned on:
$ cargo build --release
Compiling hello_world v0.1.0 (file:///path/to/package/hello_world)
cargo build --release
puts the resulting binary in target/release
instead of
target/debug
.
Compiling in debug mode is the default for development-- compilation time is shorter since the compiler doesn't do optimizations, but the code will run slower. Release mode takes longer to compile, but the code will run faster.