3-7 getaddrinfo()を利用したUDP送信プログラム

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

int
main(int argc, char *argv[])
{
  int sock;
  struct addrinfo hints, *res;
  int n;
  int err;

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

/* IPアドレス表記＋ホスト名両方に対応 */
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC; /* IPv4/IPv6両方に対応 */
hints.ai_socktype = SOCK_DGRAM;
err = getaddrinfo(argv[1], "12345", &hints, &res);
if (err != 0) {
printf("getaddrinfo : %s\n", gai_strerror(err));
return 1;
}
sock = socket(res->ai_family, res->ai_socktype, 0);
if (sock < 0) {
perror("socket");
return 1;
}
{
const char *ipverstr;
switch (res->ai_family) {
case AF_INET:
ipverstr = "IPv4";
break;
case AF_INET6:
ipverstr = "IPv6";
break;
default:
ipverstr = "unknown";
break;
}
printf("%s\n", ipverstr);
}
n = sendto(sock, "HELLO", 5, 0, res->ai_addr, res->ai_addrlen);
if (n < 1) {
perror("sendto");
return 1;
}
close(sock);
freeaddrinfo(res);
return 0;
}

拙著「Linuxネットワークプログラミング」の紹介