Finding an IP from an interface name

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

/**
 * getIPv4()
 *
 * This function takes a network identifier such as "eth0" or "eth0:0" and
 * a pointer to a buffer of at least 16 bytes and then stores the IP of that
 * device gets stored in that buffer.
 *
 * it return 0 on success or -1 on failure.
 *
 * Author:  Jaco Kroon <[email protected]>
 */
int getIPv4(const char * dev, char * ipv4) {
    struct ifreq ifc;
    int res;
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    if(sockfd < 0)
        return -1;
    strcpy(ifc.ifr_name, dev);
    res = ioctl(sockfd, SIOCGIFADDR, &ifc);
    close(sockfd);
    if(res < 0)
        return -1;
    strcpy(ipv4, inet_ntoa(((struct sockaddr_in*)&ifc.ifr_addr)->sin_addr));
    return 0;
}


int main() {
    char ip[16];
    if(getIPv4("eth0", ip) == 0)
        printf("IPv4: %sn", ip);
    else
        printf("No IPn");
    return 0;
 }

ifconfig eth0 | grep 'inet addr' | sed -e 's/:/ /' | awk '{print $3}'

ifconfig | egrep '^[^ ]' | awk '{print $1}'

for x in `ifconfig | egrep '^[^ ]' | awk '{print $1}'`; do
  echo -n "${x}"
  echo -n "    "
  ifconfig "${x}" | grep 'inet addr' | sed -e 's/:/ /' | awk '{print $3}'
done