Copyextern "C" {
    fn c_function(arg: i32) -> i32;
}

To get started, you need to ensure that you have a functioning Rust setup on your machine. You can create a new Rust project by running:

bash cargo new rust_ffi_example cd rust_ffi_example

Next, modify your Cargo.toml file to include the following settings that enable linking with C code:

toml [lib] dynamically_linked = true

Now let's define a simple C function in a separate file. Create a file named c_code.c in your project root and add the following code:

c

include <stdio.h>

int c_function(int arg) { printf("C received: %d\n", arg); return arg * 2; }

This C function takes an integer, prints it, and returns double its value.

To compile and link the C code, you'll need to include this file in your Rust build. You can do this by telling Rust to link against the C object file. Update your build.rs file (create it in the project root if it doesn’t exist) with:

rust fn main() { println!("cargo:rustc-link-search=."); println!("cargo:rustc-link-lib=static=my_c_code"); }

Ensure your C code is compiled into an object file that Rust can link against.

Now, write the main Rust function in your src/main.rs file to call this C function:

rust mod libc;

fn main() { unsafe { let result = c_function(5); println!("Result from C function: {}", result); } }

In this example, we call the c_function from the main function, passing it the integer 5.

Finally, build your project using:

bash cargo build

And run it using:

bash cargo run

You should see output similar to:

C received: 5 Result from C function: 10

This demonstrates a simple FFI interaction between Rust and C, showcasing how to effectively communicate across language boundaries.