#define _GNU_SOURCE
#include <stdlib.h>

static int f(const void *a, const void *b, void *c) {
    return 0; // not important what it does for this test
}

int main() {
    int x[4] = {3, 1, 4, 0};
    int z = 47;
    void *c = &z;
    qsort_r(x, 4, sizeof(int), f, c);
    return 0;
}