Calling External Code

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

extern "C" {
    fn abs(input: i32) -> i32;
}
fn main() {
    unsafe {
        // Undefined behavior if abs misbehaves.
        println!("Absolute value of -3 according to C: {}", abs(-3));
    }
}
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Speaker Notes

This is usually only a problem for extern functions which do things with pointers which might violate Rustโ€™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.