#include <stdio.h>

include <sys/socket.h>
include <sys/ioctl.h>
include <netinet/in.h>
include <net/if.h>
include <string.h>
include <arpa/inet.h>
int main(int argc, char **argv)
{
    int sockfd;
    struct ifreq ifr;

char *ifname="eth0";
strncpy(ifr.ifr_name, ifname, IFNAMSIZ-1);

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(ioctl(sockfd, SIOCGIFADDR, &ifr) == -1)
{
    printf("Error\n");
    return;
}

struct sockaddr_in *myaddr;
myaddr = (struct sockaddr_in*)&(ifr.ifr_addr);
printf("IP: %s\n", inet_ntoa(myaddr->sin_addr));

}</pre>