Client 這傢伙比 server 簡單多了,client 所需要做的就是:連線到你在命令列所指定的主機 3490 port,接著,client 會收到 server 送回的字串。
Client 的程式碼 [21]:
[21] http://beej.us/guide/bgnet/examples/client.c
/*/*** client.c -- 一個 stream socket client 的 demo*/#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <netdb.h>#include <sys/types.h>#include <netinet/in.h>#include <sys/socket.h>#include <arpa/inet.h>#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[]){int sockfd, numbytes;char buf[MAXDATASIZE];struct addrinfo hints, *servinfo, *p;int rv;char s[INET6_ADDRSTRLEN];if (argc != 2) {fprintf(stderr,"usage: client hostname\n");exit(1);}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));return 1;}// 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");continue;}if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {close(sockfd);perror("client: connect");continue;}break;}if (p == NULL) {fprintf(stderr, "client: failed to connect\n");return 2;}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) {perror("recv");exit(1);}buf[numbytes] = '\0';printf("client: received '%s'\n",buf);close(sockfd);return 0;}
要注意的是,你如果沒有在執行 client 以前先啟動 server 的話,connect() 會傳回 "Connection refused",這個訊息很有幫助。