mod ffi {
    unsafe extern "C++" {
        fn fallible(depth: usize) -> Result<String>;

fn main() {
    if let Err(err) = ffi::fallible(99) {
        eprintln!("Error: {}", err);
  • C++ functions declared to return a Result will catch any thrown exception on the C++ side and return it as an Err value to the calling Rust function.
  • If an exception is thrown from an extern “C++” function that is not declared by the CXX bridge to return Result, the program calls C++’s std::terminate. The behavior is equivalent to the same exception being thrown through a noexcept C++ function.