Get IP address of local network interface by getifaddrs().

get_ip.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{   
    const char* ifname = "eth0";  
    struct ifaddrs *ifaddr, *ifa;

    if(argc > 1){
        ifname = argv[1];  
    }else{
        printf("Usage:\n\t%s <eth?>\n", argv[0]);
        exit(0);
    }

    if (getifaddrs(&ifaddr) == -1) {
        perror("getifaddrs");
        exit(EXIT_FAILURE);
    }

    for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
        if((ifa->ifa_addr != NULL) &&
           (strcmp(ifa->ifa_name, ifname) == 0) &&  
           (ifa->ifa_addr->sa_family == AF_INET)) {
            printf("\tInterface: <%s>\n",ifa->ifa_name ); 
            printf("\tAddress: <%s>\n", inet_ntoa(((struct sockaddr_in *)ifa->ifa_addr)->sin_addr));
            break;
        }
    }

    freeifaddrs(ifaddr);
    exit(EXIT_SUCCESS);
}