linux c 取得 Mac address

#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;
}