Getting MAC addresses

portable_get_mac_addresses.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <ifaddrs.h>

// works on Linux and macOS
#ifdef AF_LINK
#include <net/if_dl.h>
unsigned char *get_ptr(struct ifaddrs *ifaptr)
{
  if (ifaptr->ifa_addr->sa_family == AF_LINK)
    return (unsigned char *)LLADDR((struct sockaddr_dl *)(ifaptr)->ifa_addr);
  else
    return NULL;
}
#endif
#ifdef AF_PACKET
#include <netpacket/packet.h>
unsigned char *get_ptr(struct ifaddrs *ifaptr)
{
  if (ifaptr->ifa_addr->sa_family == AF_PACKET)
    return (unsigned char *)((struct sockaddr_ll*)ifaptr->ifa_addr)->sll_addr;
  else
    return NULL;
}
#endif

// sample usage
void get_mac_address(void)
{
  struct ifaddrs *ifap;
  unsigned char *ptr;

  if (getifaddrs(&ifap) == 0) 
  {
    for (struct ifaddrs *ifaptr = ifap; ifaptr != NULL; ifaptr = ifaptr->ifa_next)
    {
      ptr = get_ptr(ifaptr);
      if (ptr != NULL) 
      {
        printf("%s: %02x:%02x:%02x:%02x:%02x:%02x\n",
               (ifaptr)->ifa_name,
               *ptr, *(ptr + 1), *(ptr + 2), *(ptr + 3), *(ptr + 4), *(ptr + 5));
      }
    }
    freeifaddrs(ifap);
  }
}