mac_addr.c

#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) {

	// 1st: ioctl -> SIOCGIFHWADDR
	mac_addr("eth0",eth0_MAC_address);
	puts(eth0_MAC_address);

	// 2nd: sysfs
	uint8_t mac[6];
	char buf[32];
	FILE *fp;
	char hostname[63] = "hostname";

	fp = fopen("/sys/class/net/eth0/address", "r");

	if (fp)
	{
		if (fgets(buf, sizeof(buf), fp) > 0)
		{
			sscanf(buf, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
					&mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]);
		}
		printf("%s-%02hhx%02hhx%02hhx%02hhx%02hhx%02hhx\n", hostname, mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
		fclose(fp);
	}

	return 0;
}