Netmask for IPv4 source

test.c

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

int main(int argc, const char * argv[]) {
    MMDB_s *mmdb = (MMDB_s *)malloc(sizeof(MMDB_s));
    MMDB_open("/tmp/GeoIP2-City_20160105/GeoIP2-City.mmdb",
              MMDB_MODE_MMAP, mmdb);
    
    int gai_error = 0;
    int mmdb_error = MMDB_SUCCESS;
    MMDB_lookup_result_s res = MMDB_lookup_string(mmdb, "71.183.42.223", &gai_error, &mmdb_error);
    
    // Result from legacy database is:  71.183.42.223 = 24
    // The following returns:  Netmask as returned: 120, corrected: 24
    printf("Netmask as returned: %d, corrected: %d\n", res.netmask, res.netmask - mmdb->ipv4_start_node.netmask);
    
    return 0;
}