how do 2?

gistfile1.rs

extern crate libc;

use libc::*;
use std::ptr;

#[allow(non_camel_case_types)]
#[repr(C)]
type krb5_error_code = c_uint;

#[allow(non_camel_case_types)]
#[repr(C)]
struct krb5_context;

impl krb5_context {
    fn new<'a>() -> &'a krb5_context {
        unsafe {
            &*ptr::null()
        }
    }
}

impl Drop for krb5_context {
    fn drop(&mut self) {
        unsafe{
            krb5_free_context(self)
        }
    }
}

#[link(name = "krb5")]
extern "C" {
    fn krb5_init_context(context: *mut krb5_context) -> krb5_error_code;
    fn krb5_free_context(context: *mut krb5_context);
}

fn main() {
    let res = unsafe {
        let mut ctx = krb5_context::new();
        if krb5_init_context(ctx) == 0 {
            Ok(())
        } else {
            Err(())
        }
    };
    // match res {
    //     Ok(_) => println!("SUCCESS!"),
    //     Err(_) => println!("ERROR!"),
    // }
}