Get IP address of an interface on linux

Question

How can I get the IPv4 address of an interface in linux from C code ?

e.g. I'd like to get the IP address(if any) assigned to eth0

Answer 1

I found this page see if it has what you need.

Answer 2

Try this:

#include <stdio.h>

#include <string.h> /* for strncpy */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>

int
main()
{
 int fd;
 struct ifreq ifr;

 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 "eth0" */
 strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1);

 ioctl(fd, SIOCGIFADDR, &ifr);

 close(fd);

 /* display result */
 printf("%s\n", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));

 return 0;
}

The code sample is take from here.

Answer 3

In addition to the ioctl() method Filip demonstrated you can use getifaddrs(). There is an example program at the bottom of the man page.