인터페이스의 ip 알려주는 함수 알려주세요.

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <net/if.h>

#define ADDR_MAX        32

int
main(int argc, char *argv[])
{
  int fd;
  struct ifreq ifr;
  struct sockaddr_in *aptr;

  char address[ADDR_MAX] = { 0, };

  if (argc != 2) {
    fprintf(stderr, "usage: %s INTERFACE\n", argv[0]);
    return 1;
  }

  fd = socket(AF_INET, SOCK_DGRAM, 0);
  if (fd < 0) {
    fprintf(stderr, "socket(2) failed\n");
    return 1;
  }

  strncpy(ifr.ifr_name, argv[1], IFNAMSIZ);

  if (ioctl(fd, SIOCGIFADDR, &ifr) < 0) {
    fprintf(stderr, "ioctl(2) failed\n");
    return 1;
  }

  aptr = (struct sockaddr_in *)&ifr.ifr_addr;
  inet_ntop(AF_INET, &aptr->sin_addr, address, ADDR_MAX);
  printf("%s - %s\n", argv[1], address);

  return 0;
}

$ ./a.out lo
lo - 127.0.0.1
$ ./a.out eth0
eth0 - 168.219.193.75
$ ./a.out eth1
eth1 - 192.168.0.1