Get IP address of an interface on Linux

Question

How can I get the IPv4 address of an interface on Linux from C code?

For example, I'd like to get the IP address (if any) assigned to eth0.

Answer 1

Try this:

#include <stdio.h> #include <unistd.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> #include <arpa/inet.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 taken from here.

Answer 2

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