3-18 UDPパケットの送信&受信プログラム

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
void
print_my_port_num(int sock)
{
struct sockaddr_in s;
socklen_t sz = sizeof(s);
getsockname(sock, (struct sockaddr *)&s, &sz);
printf("%d\n", ntohs(s.sin_port));
}
int
main(int argc, char *argv[])
{
int sock;
struct sockaddr_in addr;
struct sockaddr_in senderinfo;
socklen_t senderinfolen;
int n;
char buf[2048];
if (argc != 2) {
fprintf(stderr, "Usage : %s dstipaddr\n", argv[0]);
return 1;
}
sock = socket(AF_INET, SOCK_DGRAM, 0);
addr.sin_family = AF_INET;
addr.sin_port = htons(12345);
inet_pton(AF_INET, argv[1], &addr.sin_addr.s_addr);
n = sendto(sock, "HELLO", 5, 0, (struct sockaddr *)&addr, sizeof(addr));
if (n < 1) {
perror("sendto");
return 1;
}
print_my_port_num(sock);
memset(buf, 0, sizeof(buf));
senderinfolen = sizeof(senderinfo);
recvfrom(sock, buf, sizeof(buf), 0,
(struct sockaddr *)&senderinfo, &senderinfolen);
printf("%s\n", buf);
close(sock);
return 0;
}

拙著「Linuxネットワークプログラミング」の紹介