#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main(void)
{
    const char *ip6str = "2a03:6300:1:103:211:5bff:fe31:13e1";
    const char *first = "2a03:6300:1:103:218:5bff:fe31:13e1";
    const char *last = "2a03:6300:1:103:220:5bff:fe31:13e1";

    struct in6_addr result, resfirst, reslast;

    inet_pton(AF_INET6, first, &resfirst);
    inet_pton(AF_INET6, last, &reslast);
    inet_pton(AF_INET6, ip6str, &result);

    if (memcmp(&result, &resfirst, sizeof(result)) > 0 && memcmp(&result, &reslast, sizeof(result)) < 0 ) {
        printf("OOOK\n");
    }

    return 0;
}