#include <stdio.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <net/ethernet.h>

#define ETH_ABUFLEN ((ETH_ALEN*2)+1)

void mac_addr(const char* name, unsigned char MAC_str[ETH_ABUFLEN])
{
    int s,i;
    struct ifreq ifr;
    MAC_str[0]='\0';
    if ((s=socket(AF_INET, SOCK_DGRAM, 0)) != -1) {
        strcpy(ifr.ifr_name, name);
        if (ioctl(s, SIOCGIFHWADDR, &ifr) != -1) {
            for (i=0; i<ETH_ALEN; i++)
                sprintf(&MAC_str[i*2],"%02X",((unsigned char*)ifr.ifr_hwaddr.sa_data)[i]);
        }
        close(s);
    }
    MAC_str[ETH_ABUFLEN-1]='\0';
}

unsigned char eth0_MAC_address[ETH_ABUFLEN];

int main(void) {
    mac_addr("eth0",eth0_MAC_address);
    puts(eth0_MAC_address);
}