Use ioctl to set the mac address to obtain the current IP address, subnet mask, and other information.

 #include <sys/types.h>  /* for socket(2) and related bits and pieces */
#include <sys/socket.h> /* for socket(2) */
#include <net/if.h>     /* for struct ifreq */
#include <net/if_arp.h> /* for ARPHRD_ETHER */
#include <sys/ioctl.h>  /* for IOCTL's */
#include <stdio.h>      /* for fprintf etc */
#include <unistd.h>     /* for close */


int main(int argc,char **argv)
{
    struct ifreq ifr;
    int skfd;

    if (argc<3) {
        fprintf(stderr,"usage:/n%s interface hwaddr/n",argv[1]);
        return 1;
    }

    /* Fill in the structure */
    snprintf(ifr.ifr_name, IFNAMSIZ, "%s", argv[1]);
    ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;

    /* TODO: write some code to parse argv[2] into ifr.ifr_hwaddr.sa_data */
    /* memcpy(&ifr.ifr_hwaddr.sa_data, argv[2], sizeof(ether.address)); */
    /* Create a socket fd */
    skfd = socket(PF_INET,SOCK_STREAM,0);

    /* call the IOCTL */
    if (ioctl(skfd, SIOCSIFHWADDR, &ifr) < 0) {
        perror("ioctl(SIOCSIFHWADDR)");
        return 1;
    }

    /* cleanup */
    close(skfd);

    /* we're out of here! */
    return 0;
}

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

static void usage(){
    printf("usage : ipconfig interface /n");
    exit(0);
}

int main(int argc,char **argv)
{
    struct sockaddr_in *addr;
    struct sockaddr     sa;   
    struct ifreq ifr;
    char *name,*address;
    int sockfd;
    unsigned   char   mac[6];

    if(argc != 2) 
         usage();
    else
         name = argv[1];

    sockfd = socket(AF_INET,SOCK_DGRAM,0);
    strncpy(ifr.ifr_name,name,IFNAMSIZ-1);

    if(ioctl(sockfd,SIOCGIFADDR,&ifr) == -1)
         perror("ioctl error"),exit(1);

    addr = (struct sockaddr_in *)&(ifr.ifr_addr);
    address = inet_ntoa(addr->sin_addr);
    printf("inet addr: %s ",address);

    if(ioctl(sockfd,SIOCGIFBRDADDR,&ifr) == -1)
         perror("ioctl error"),exit(1);

    addr = (struct sockaddr_in *)&ifr.ifr_broadaddr;
    address = inet_ntoa(addr->sin_addr);
    printf("broad addr: %s ",address);

    if(ioctl(sockfd,SIOCGIFNETMASK,&ifr) == -1)
         perror("ioctl error"),exit(1);

    addr = (struct sockaddr_in *)&ifr.ifr_addr;
    address = inet_ntoa(addr->sin_addr);
    printf("inet mask: %s ",address);

    printf("/n");
    if(ioctl(sockfd, SIOCGIFHWADDR, &ifr) == -1)
         perror("ioctl error"), exit(1);

    memcpy(&sa,   &ifr.ifr_addr,   sizeof(struct   sockaddr_in));
    memcpy(mac,   sa.sa_data,   sizeof(mac));
    fprintf(stdout,   "%s   mac:   %.2X:%.2X:%.2X:%.2X:%.2X:%.2X/n",
            name,   mac[0],   mac[1],   mac[2],   mac[3],   mac[4],   mac[5]);

    exit(0);
}