use libc::c_char;
use std::ffi::CStr;

type GiveCChar = extern "C" fn(*const c_char);

extern "C" {
    fn hello(give_c_char: GiveCChar);
}

fn main() {
    unsafe { hello(print_cstr); }
}

extern "C" fn print_cstr(c: *const c_char) {
    let x = unsafe { CStr::from_ptr(c) };
    println!("{:?}", x);
}