Use C language to get MAC Address in linux

#include <stdio.h>
#include <string.h> /* for strncpy */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>

int main(void) {
    int fd;
    struct ifreq ifr;

    char mac[20];
    fd = socket(AF_INET, SOCK_DGRAM, 0);

    ifr.ifr_addr.sa_family = AF_INET;
    strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1);

    ioctl(fd, SIOCGIFHWADDR, &ifr);

    close(fd);

    sprintf(mac,"%.2x:%.2x:%.2x:%.2x:%.2x:%.2x",
         (unsigned char)ifr.ifr_hwaddr.sa_data[0],
         (unsigned char)ifr.ifr_hwaddr.sa_data[1],
         (unsigned char)ifr.ifr_hwaddr.sa_data[2],
         (unsigned char)ifr.ifr_hwaddr.sa_data[3],
         (unsigned char)ifr.ifr_hwaddr.sa_data[4],
         (unsigned char)ifr.ifr_hwaddr.sa_data[5]);

    printf("eth0 mac address:%s\n", mac);

    return 0;
}