** client.c -- 一個 stream socket client 的 demo
#define PORT "3490" // Client 所要連線的 port
#define MAXDATASIZE 100 // 我們一次可以收到的最大位原組數(number of bytes)
// 取得 IPv4 或 IPv6 的 sockaddr:
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);
int main(int argc, char *argv[])
struct addrinfo hints, *servinfo, *p;
char s[INET6_ADDRSTRLEN];
fprintf(stderr,"usage: client hostname\n");
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
// 用迴圈取得全部的結果,並先連線到能成功連線的
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("client: socket");
if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
perror("client: connect");
fprintf(stderr, "client: failed to connect\n");
inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof s);
printf("client: connecting to %s\n", s);
freeaddrinfo(servinfo); // 全部皆以這個 structure 完成
if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
printf("client: received '%s'\n",buf);