prng_bleagh.c

/* MacOS libc PRNG is garbage!
 * Test this on MacOS 10.12.3 (may be the same with other versions)
 * You'll see three times the same output.
 * Cheers by @antirez. */

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    /* Note, 1000000, 1000001, 1000002 are not special.
     * You can use any other "near" seeds and MOD 7 the sequence will be the same. */
    srand(1000000);
    printf("%d\n", rand() % 7);
    srand(1000001);
    printf("%d\n", rand() % 7);
    srand(1000002);
    printf("%d\n", rand() % 7);
    return 0;
}

@colmmacc read my last post. You misunderstood the point completely. Happens for every possible N seeds that are just similar numbers.

TLDR: it happens even with this code.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    int seed = time(NULL);
    srand(seed+1);
    printf("%d\n", rand() % 7);
    srand(seed+2);
    printf("%d\n", rand() % 7);
    srand(seed+10);
    printf("%d\n", rand() % 7);
    return 0;
}