Calling External Code

Functions from other languages might violate the guarantees of Rust. Calling them is thus unsafe:

1. extern "C" {
2. fn abs(input: i32) -> i32;
3. }

5. fn main() {
6. unsafe {
7. // Undefined behavior if abs misbehaves.
8. println!("Absolute value of -3 according to C: {}", abs(-3));
9. }
10. }

This is usually only a problem for extern functions which do things with pointers which might violate Rust’s memory model, but in general any C function might have undefined behaviour under any arbitrary circumstances.

The "C" in this example is the ABI; other ABIs are available too.