Get Address of a Network Interface in C

So, here I am searching the internet over and over again to find out how to easily and quickly get the ip address of a local interface, and there isn't an easy way to do it without running `ifconfig | grep | cut...` in some crazy fashion.

So, here I've compiled a simple C script that will iterate through your interfaces and get the IP address of a local network interface if you supply it on the command line.

Feel free to redistribute under GNU.

https://github.com/markizano/scripts/blob/master/getifaddr/getifaddr.c

/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.


I am not the original author of this script. This was inspired by
the man page at getifaddrs(3).
*/

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

int Usage () {
printf("Usage: getifaddr [ifaddr] [inet|inet6]\nDefaults to eth0/inet.\n");
return 8;
}

int main(int argc, char *argv[]) {
struct ifaddrs *ifaddr, *ifa;
int family, s, inet;
char host[NI_MAXHOST], *iface;

iface = NULL; inet = AF_INET;
if ( argc >= 2 ) {
if ( !strcmp(argv[1], "-h") || !strcmp(argv[1], "--help") ) {
return Usage();
}
} else if ( argc <= 2 ) {
return Usage();
}

if ( argc >= 2 ) {
iface = strndup(argv[1], strlen(argv[1]));
}

if ( argc >= 3 ) {
if ( !strcmp(argv[2], "inet6") ) {
inet = AF_INET6;
}
}

if ( iface == NULL ) {
iface = malloc(4);
if ( iface == NULL ) return 4;
strncpy(iface, "eth0", 4);
}

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

memset(host, 0, sizeof host);

/* Walk through linked list, maintaining head pointer so we can free list later */

for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
if (ifa->ifa_addr == NULL) continue;
family = ifa->ifa_addr->sa_family;

if ( family == AF_PACKET ) continue;

/* Display interface name and family (including symbolic
form of the latter for the common families) */
if ( !strcmp(ifa->ifa_name, iface) ) {
if ( family == inet ) {
s = getnameinfo(ifa->ifa_addr, ( (family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6) ), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if (s != 0) {
fprintf(stderr, "getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
}

printf( "%s\n", host );
freeifaddrs(ifaddr);
free(iface);
return 0;
}
}

fprintf(stderr, "Could not find devivce.\n");
freeifaddrs(ifaddr);
free(iface);
exit(EXIT_SUCCESS);
}

Comments

Popular posts from this blog

Setup and Install Monero(d) -- p2pool -- xmrig

Build xmrig on Linux

Git: Process