ソースコード例：インターフェース一覧表示

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <errno.h>

#define MAX_IFR 8

static int ifstatus(int sk, char *name) {
	char		buf[INET_ADDRSTRLEN + 1];
	struct ifreq	ifr;
	struct sockaddr_in *s_in;

	strncpy(ifr.ifr_name, name, IFNAMSIZ-1);
	ifr.ifr_addr.sa_family = AF_INET;
	ioctl(sk, SIOCGIFFLAGS, &ifr);
	if(ifr.ifr_flags & IFF_UP) {
		s_in = (struct sockaddr_in *)&ifr.ifr_addr;
		s_in->sin_family = AF_INET;
		ioctl(sk, SIOCGIFADDR, &ifr);
		inet_ntop(AF_INET, &s_in->sin_addr.s_addr, buf, INET_ADDRSTRLEN);
		printf("%s:\tinet %s", ifr.ifr_name, buf);
		ioctl(sk, SIOCGIFNETMASK, &ifr);
		inet_ntop(AF_INET, &s_in->sin_addr.s_addr, buf, INET_ADDRSTRLEN);
		printf("  netmask %s", buf);
		ioctl(sk, SIOCGIFHWADDR, &ifr);
		printf("  ether %.2x:%.2x:%.2x:%.2x:%.2x:%.2x\n",
		  (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]);
	}

}

static int ifdown(int sk, char *name) {
	struct ifreq		ifr;
	struct sockaddr_in	*s_in;

	strncpy(ifr.ifr_name, name, IFNAMSIZ-1);
	ifr.ifr_addr.sa_family = AF_INET;
	ioctl(sk, SIOCGIFFLAGS, &ifr);
	ifr.ifr_flags &= ~IFF_UP;
	ioctl(sk, SIOCSIFFLAGS, &ifr);
	return 0;
}

static int ifup(int sk, char *name, char *addr, char *mask) {
	int			ret;
	struct ifreq		ifr;
	struct sockaddr_in	*s_in;

	strncpy(ifr.ifr_name, name, IFNAMSIZ-1);
	ret = ioctl(sk, SIOCGIFFLAGS, &ifr);
	if(ret == -1) {
		perror("error");
		return -1;
	}
	ifr.ifr_flags |= IFF_UP;
	ioctl(sk, SIOCSIFFLAGS, &ifr);
	s_in = (struct sockaddr_in *)&ifr.ifr_addr;
	s_in->sin_family = AF_INET;
	s_in->sin_addr.s_addr = inet_addr(addr);
	ioctl(sk, SIOCSIFADDR, &ifr);
	s_in->sin_addr.s_addr = inet_addr(mask);
	ioctl(sk, SIOCSIFNETMASK, &ifr);
	return 0;
}

int main(int argc, char **argv) {
	int		sk, ret, nifs, i;
	struct ifreq	ifrs[MAX_IFR];
	struct ifconf	ifc;

	sk = socket(AF_INET, SOCK_DGRAM, 0);
	if(sk == -1) {
		perror("error");
		return -1;
	}

	if(argc == 1) {
		ifc.ifc_len = sizeof(ifrs);
		ifc.ifc_ifcu.ifcu_buf = (void *)ifrs;
		ioctl(sk, SIOCGIFCONF, &ifc);
		nifs = ifc.ifc_len / sizeof(struct ifreq);
		for(i = 0;i < nifs;i++) {
			ifstatus(sk, ifrs[i].ifr_name);
		}
	} else if(argc == 2) {
		ifstatus(sk, argv[1]);
	} else if(argc == 3) {
		if(strcmp(argv[2], "down") == 0) {
			ifdown(sk, argv[1]);
		} else {
			ifup(sk, argv[1], argv[2], "255.255.255.0");		
		}
		ifstatus(sk, argv[1]);
	} else if(argc == 4) {
		ifup(sk, argv[1], argv[2], argv[3]);		
		ifstatus(sk, argv[1]);
	}
	close(sk);
	return 0;
}