fetch if addr

ifaddr.c

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

struct if_info {
    char if_name[IFNAMSIZ];
    u_int8_t ipaddr[4];
    u_int8_t hwaddr[ETH_ALEN];
};

void fill_if_info(const char* if_name,struct if_info* ifr_info)
{
    int s;
    struct ifreq ifr;
    struct sockaddr_in *saddr;

    /* copy the interface name */ 
    strcpy(ifr_info->if_name,if_name);

    /* create a socket for ioctl operations */
    s = socket(AF_INET,SOCK_STREAM,0);

    /* copy the interface name to ifreq.if_name */
    strcpy(ifr.ifr_name, if_name);

    /* do an ioctl to get ipaddress */
    ioctl(s, SIOCGIFADDR, &ifr);
    saddr = (struct sockaddr_in*) &ifr.ifr_addr;
    memcpy(&ifr_info->ipaddr, &saddr->sin_addr, sizeof(ifr_info->ipaddr));

    /* do an ioctl to get hardware address*/
    ioctl(s, SIOCGIFHWADDR, &ifr);
    memcpy(ifr_info->hwaddr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
}

void print_if_info(struct if_info* a)
{
    printf(" device: %s.\n", a->if_name);
    printf(" ipaddr: %u.\n", a->ipaddr[0]);
    printf(" hwaddr: %02x:%02x:%02x:%02x:%02x:%02x.\n",a->hwaddr[0],
                                                       a->hwaddr[1],
                                                       a->hwaddr[2],
                                                       a->hwaddr[3],
                                                       a->hwaddr[4],
                                                       a->hwaddr[5]);
}
int main(int argc, char *argv[])
{
    struct if_info a;
    if(argc != 2) return 1;
    fill_if_info(argv[1],&a);
    print_if_info(&a);
    return 0;
}