Why crypt_data isn't known?

Question

regarding to the man page of crypt_r() of freeBSD all I need to include is

#define _GNU_SOURCE
#include <crypt.h>

But it doesn't run. I ofcourse also linked -lcrypt

#define _XOPEN_SOURCE
#include <unistd.h>
#define _GNU_SOURCE
#include <crypt.h>
#include "ownstuff"

int CreateUser (some stuff)
{
    //struct crypt_data data; Also didn't work
    crypt_data data;
    char *res;
    data.initialized = 0;

    res = crypt_r("password", "$6$QX", &data);

    return 0;
}

So what's wrong? I don't get it.

EDIT:

Also changing the header part to this:

#define _XOPEN_SOURCE
#include <unistd.h>
#include "ownstuff"

Didn't change anything from the error it self.