Build the C Library

Sadly, simply having a .c file in your project isn't enough to make it work.

Note: this is where we find out if everyone's laptop has the right software installed!

There's a lot of ways to build a C library. It's one of the reasons to love Cargo! We're going to use the cc crate, which will try its very best to find a workable C compiler on your system, invoke it to build the library, and link it to your Rust program.

First, add the cc crate to your Cargo.toml:

[build-dependencies]
cc = "1.0"

Now we're going to make a build.rs file. If you haven't used build.rs before, it's a special file that Cargo will run before building your project.

In the root of your project (NOT the src directory), make a new file named build.rs:

fn main() {
    cc::Build::new()
        .file("src/hello.c")
        .compile("hello");
}

Your tree should look like this:

.
├── build.rs
├── Cargo.toml
└── src
    ├── hello.c
    └── main.rs

So, let's see what happens! If all goes well:

cargo run
Hello, world!

And hidden in your target/debug directory there's even a libhello.a - a static C library.

But What If It Doesn't Work?

This is the fun part. If you don't have a C compiler installed, it's not a C compiler that Rust can find, you'll have a not overly helpful error message.

• On Windows, you need the Build Tools for Visual Studio.
• On Mac, you need to install the Xcode Command Line Tools. You can do this by running xcode-select --install in your terminal.
• On Linux, you need to install build-essential. I personally like to install clang as well.