id.rs

// The C method signature is as follows:

int
getgrouplist(const char *name, int basegid, int *groups, int *ngroups);

// My Rust extern block

extern {
fn getgrouplist(name: *libc::c_char,
                    basegid: libc::c_int,
                    groups: *mut libc::c_int,
                    ngroups: *mut libc::c_int) -> libc::c_int;
}

// Trying to use it
let groups = 0;
let num_groups = 0;
// How do I setup a pointer to integer type ?
unsafe {
    getgrouplist((*pw).pw_name, (*pw).pw_gid, &mut groups, &mut num_groups);
}