The “cxx” library is a Rust library created by dtolnay that provides safe interoperation between Rust and C++. It allows developers to call C++ code from Rust and vice versa, making it possible to seamlessly integrate existing C++ codebases and libraries into Rust projects.


The purpose of the cxx library is to provide a convenient and safe way to interact between Rust and C++. It abstracts away many of the complexities of interfacing between the two languages, making it easier for developers to work with existing C++ code or to use C++ libraries and tools within Rust projects.


  • Provides a convenient way to call C++ functions from Rust
  • Makes it possible to pass data between Rust and C++ safely
  • Abstracts away low-level details of interoperation between Rust and C++
  • Supports a variety of use cases, such as calling C++ libraries from Rust and vice versa


  • Makes it easier to integrate existing C++ code into Rust projects
  • Facilitates the use of C++ libraries and tools within Rust projects
  • Provides a safe and convenient way to interface between Rust and C++
  • Helps to minimize the risk of errors and bugs when working with both languages

Here is an example of how you could use the cxx library to call a C++ function from Rust:

And here is an example of how you could call this C++ function from Rust using the cxx library:


use cxx::bridge;
use cxx::bridge::CppBox;
mod ffi {
extern “C” {
fn cpp_function(message: *const c_char);

fn main() {
let message = CppBox::new(“Hello from Rust!”);
unsafe {

This code defines a simple C++ function cpp_function that takes a string as an argument and outputs it to the console. It then defines a Rust module ffi that bridges this C++ function into Rust using the cxx library. Finally, the Rust code creates a new string, passes it to the C++ function, and outputs the message “Hello from Rust!” to the console.


The cxx library provides a valuable tool for Rust developers looking to interact with C++ code. It abstracts away many of the complexities of working with two different languages, making it easier to write safe and effective code that integrates Rust and C++. If you’re working with both languages, it’s worth considering the cxx library as a solution for interoperation.