Simple program to return the IP address of an interface.

#include <stdio.h>
#include <string.h> /* for strncpy */
#include <unistd.h> // for close
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>
 
#define BUF 0x05 
int main(int argc, char **argv) {
	int fd;
	struct ifreq ifr;
	char* myarg = argv[1];
	char* myarg1 = argv[2];
 
	if (!myarg || !myarg1) {
		printf("Simple IP information.\n");
		printf("Usage: --ip <IFACE>\n");
	}
 
	if (argc > 1 && strncmp(argv[1], "--ip", BUF) == 0) {
 
		fd = socket(AF_INET, SOCK_DGRAM, 0);
		/* I want to get an IPv4 IP address */
		ifr.ifr_addr.sa_family = AF_INET;
 
		/* I want IP address attached to the specified interface... */
		strncpy(ifr.ifr_name, myarg1, IFNAMSIZ-1);
 
		ioctl(fd, SIOCGIFADDR, &ifr);
 
		close(fd);
 
		/* display result */
		fprintf(stdout, "IP information.\n");
		printf("%s\n", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));
	}
 
	return 0;
}