lib.rs

extern crate libc;
use libc::*;
#[no_mangle]
pub unsafe extern "C" fn example(src: *mut u8, len : size_t) -> c_int{
    if (!src.is_null()) {
        *src = 1u8;
    }
    let k = len - 1;
    *src.offset(k as isize) = 1u8; // if we comment this line unresolved external will dissapear
    return 0;
}