创建一个连接UDP套接口的客户端,代码如下:
#include <netdb.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#define MAXLINE 128
int udp_connect(const char *host, const char *serv)
{
int sockfd, n;
struct addrinfo hints, *res, *ressave;
bzero(&hints, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM;
if ((n = getaddrinfo(host, serv, &hints, &res)) != 0) {
printf("udp_connect error for %s, %s:%s\n", host, serv, gai_strerror(errno));
return -1;
}
ressave = res;
do {
sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (sockfd < 0) continue;
if (connect(sockfd, res->ai_addr, res->ai_addrlen) == 0) break;
close(sockfd);
} while ((res = res->ai_next) != NULL);
if (res == NULL) {
printf("udp_connect error for %s, %s\n", host, serv);
return -1;
}
freeaddrinfo(ressave);
return sockfd;
}
char *sock_ntop(const struct sockaddr* sa, socklen_t len)
{
char portstr[7];
static char str[MAXLINE + 1];
switch (sa->sa_family) {
case AF_INET:
{
struct sockaddr_in *sin = (struct sockaddr_in*)sa;
if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str)) == NULL) return NULL;
if (ntohs(sin->sin_port) != 0) {
snprintf(portstr, sizeof(portstr), ":%d", ntohs(sin->sin_port));
strcat(str, portstr);
}
return str;
}
}
return NULL;
}
int main(int argc, char **argv)
{
int sockfd, n;
char recvline[MAXLINE + 1];
socklen_t salen;
struct sockaddr *sa;
if (argc != 3) {
printf("usage:exename <hostname/ipaddress> <sevice/port>\n");
return -1;
}
sockfd = udp_connect(argv[1], argv[2]);
//printf("sending to %s\n", sock_ntop(sa, salen));
send(sockfd, " ", 1, 0);
n = recv(sockfd, recvline, MAXLINE, 0);
recvline[n] = 0;
fputs(recvline, stdout);
return 0;
}