如何从C程序输出主机的IP地址？

#include <stdio.h>#include <stropts.h>#include <sys/socket.h>#include <sys/ioctl.h>#include <linux/netdevice.h>#include <arpa/inet.h>#include <netinet/in.h>#include <unistd.h>int print_addresses(const int domain){  int s;  struct ifconf ifconf;  struct ifreq ifr[50];  int ifs;  int i;  s = socket(domain, SOCK_STREAM, 0);  if (s < 0) {    perror("socket");    return 0;  }  ifconf.ifc_buf = (char *) ifr;  ifconf.ifc_len = sizeof ifr;  if (ioctl(s, SIOCGIFCONF, &ifconf) == -1) {    perror("ioctl");    return 0;  }  ifs = ifconf.ifc_len / sizeof(ifr[0]);  printf("interfaces = %d:n", ifs);  for (i = 0; i < ifs; i++) {    char ip[INET_ADDRSTRLEN];    struct sockaddr_in *s_in = (struct sockaddr_in *) &ifr[i].ifr_addr;    if (!inet_ntop(domain, &s_in->sin_addr, ip, sizeof(ip))) {      perror("inet_ntop");      return 0;    }    printf("%s - %sn", ifr[i].ifr_name, ip);  }  close(s);  return 1;}int main(int argc, char *argv[]){  int domains[] = { AF_INET, AF_INET6 };  int i;  for (i = 0; i < sizeof(domains) / sizeof(domains[0]); i++)    if (!print_addresses(domains[i]))      return 1;  return 0;}