呼叫外部程式碼

其他語言的函式可能會違反 Rust 保證，因此呼叫這類函式並不安全：

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));
    }
}

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.

此例中的 "C" 為 ABI；您也可以使用其他 ABI。