** listener.c -- 一個 datagram sockets "server" 的 demo
#define MYPORT "4950" // 使用者所要連線的 port
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
return &(((struct sockaddr_in6*)sa)->sin6_addr);
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr;
char s[INET6_ADDRSTRLEN];
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // 設定 AF_INET 以強制使用 IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // 使用我的 IP
if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
// 用迴圈來找出全部的結果,並 bind 到首先找到能 bind 的
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("listener: socket");
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
perror("listener: bind");
fprintf(stderr, "listener: failed to bind socket\n");
printf("listener: waiting to recvfrom...\n");
addr_len = sizeof their_addr;
if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
(struct sockaddr *)&their_addr, &addr_len)) == -1) {
printf("listener: got packet from %s\n",
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr), s, sizeof s));
printf("listener: packet is %d bytes long\n", numbytes);
printf("listener: packet contains \"%s\"\n", buf);