#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define SIZE 1024
int main(int argc, char *argv[])
{
int sd, ret;
struct sockaddr_in peer;
char buffer[SIZE];
if (argc < 4) return -1;
sd = socket(PF_INET, SOCK_DGRAM, 0);
peer.sin_family = AF_INET;
peer.sin_port = htons(atoi(argv[2]));
inet_pton(AF_INET, argv[1], &peer.sin_addr);
ret = sendto(sd, argv[3], strlen(argv[3]) + 1, 0,
(struct sockaddr *)&peer, sizeof(peer));
ret = recvfrom(sd, buffer, SIZE, 0, NULL, NULL);
printf("loop back: %d, %s\n", ret, buffer);
close(sd);
return 0;
}