本章节是用基本的Linux/Unix基本函数加上select调用编写一个完整的服务器和客户端例子，可在Linux(ubuntu)和Unix(freebsd)上运行，客户端和服务端的功能如下:
客户端从标准输入读入一行，发送到服务端
服务端从网络读取一行，然后输出到客户端
客户端收到服务端的响应，输出这一行到标准输出
代码如下:
#include <unistd.h>
#include <sys/types.h> /* basic system data types */
#include <sys/socket.h> /* basic socket definitions */
#include <netinet/in.h> /* sockaddr_in{} and other Internet defns */
#include <arpa/inet.h> /* inet(3) functions */
#include <sys/select.h> /* select function*/
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#define MAXLINE 10240
void handle(int * clientSockFds, int maxFds, fd_set* pRset, fd_set* pAllset);
int main(int argc, char **argv)
{
int servPort = 6888;
int listenq = 1024;
int listenfd, connfd;
struct sockaddr_in cliaddr, servaddr;
socklen_t socklen = sizeof(struct sockaddr_in);
int nready, nread;
char buf[MAXLINE];
int clientSockFds[FD_SETSIZE];
fd_set allset, rset;
int maxfd;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
if (listenfd < 0) {
perror("socket error");
return -1;
}
int opt = 1;
if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
perror("setsockopt error");
}
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(servPort);
if(bind(listenfd, (struct sockaddr*)&servaddr, socklen) == -1) {
perror("bind error");
exit(-1);
}
if (listen(listenfd, listenq) < 0) {
perror("listen error");
return -1;
}
int i = 0;
for (i = 0; i< FD_SETSIZE; i++)
clientSockFds[i] = -1;
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
maxfd = listenfd;
printf("echo server use select startup, listen on port %d\n", servPort);
printf("max connection: %d\n", FD_SETSIZE);
for ( ; ; ) {
rset = allset;
nready = select(maxfd + 1, &rset, NULL, NULL, NULL);
if (nready < 0) {
perror("select error");
continue;
}
if (FD_ISSET(listenfd, &rset)) {
connfd = accept(listenfd, (struct sockaddr*) &cliaddr, &socklen);
if (connfd < 0) {
perror("accept error");
continue;
}
sprintf(buf, "accept form %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port);
printf(buf, "");
for (i = 0; i< FD_SETSIZE; i++) {
if (clientSockFds[i] == -1) {
clientSockFds[i] = connfd;
break;
}
}
if (i == FD_SETSIZE) {
fprintf(stderr, "too many connection, more than %d\n", FD_SETSIZE);
close(connfd);
continue;
}
if (connfd > maxfd)
maxfd = connfd;
FD_SET(connfd, &allset);
if (--nready <= 0)
continue;
}
handle(clientSockFds, maxfd, &rset, &allset);
}
}
void handle(int * clientSockFds, int maxFds, fd_set* pRset, fd_set* pAllset) {
int nread;
int i;
char buf[MAXLINE];
for (i = 0; i< maxFds; i++) {
if (clientSockFds[i] != -1) {
if (FD_ISSET(clientSockFds[i], pRset)) {
nread = read(clientSockFds[i], buf, MAXLINE);//读取客户端socket流
if (nread < 0) {
perror("read error");
close(clientSockFds[i]);
FD_CLR(clientSockFds[i], pAllset);
clientSockFds[i] = -1;
continue;
}
if (nread == 0) {
printf("client close the connection\n");
close(clientSockFds[i]);
FD_CLR(clientSockFds[i], pAllset);
clientSockFds[i] = -1;
continue;
}
write(clientSockFds[i], buf, nread);//响应客户端 有可能失败，暂不处理
}
}
}
}
代码如下:
#include <unistd.h>
#include <sys/types.h> /* basic system data types */
#include <sys/socket.h> /* basic socket definitions */
#include <netinet/in.h> /* sockaddr_in{} and other Internet defns */
#include <arpa/inet.h> /* inet(3) functions */
#include <sys/select.h> /* select function*/
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#define MAXLINE 10240
#define max(a,b) ((a) > (b) ? (a) : (b))
//typedef struct sockaddr SA;
void handle(int sockfd);
int main(int argc, char **argv)
{
char * servInetAddr = "127.0.0.1";
int servPort = 6888;
char buf[MAXLINE];
int connfd;
struct sockaddr_in servaddr;
if (argc == 2) {
servInetAddr = argv[1];
}
if (argc == 3) {
servInetAddr = argv[1];
servPort = atoi(argv[2]);
}
if (argc > 3) {
printf("usage: selectechoclient <IPaddress> <Port>\n");
return -1;
}
connfd = socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(servPort);
inet_pton(AF_INET, servInetAddr, &servaddr.sin_addr);
if (connect(connfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
perror("connect error");
return -1;
}
printf("welcome to selectechoclient\n");
handle(connfd); /* do it all */
close(connfd);
printf("exit\n");
exit(0);
}
void handle(int connfd)
{
FILE* fp = stdin;
char sendline[MAXLINE], recvline[MAXLINE];
fd_set rset;
FD_ZERO(&rset);
int maxfds = max(fileno(fp), connfd) + 1;
int nread;
for (;;) {
FD_SET(fileno(fp), &rset);
FD_SET(connfd, &rset);
if (select(maxfds, &rset, NULL, NULL, NULL) == -1) {
perror("select error");
continue;
}
if (FD_ISSET(connfd, &rset)) {
//接收到服务器响应
nread = read(connfd, recvline, MAXLINE);
if (nread == 0) {
printf("server close the connection\n");
break;
}
else if (nread == -1) {
perror("read error");
break;
}
else {
//server response
write(STDOUT_FILENO, recvline, nread);
}
}
if (FD_ISSET(fileno(fp), &rset)) {
//标准输入可读
if (fgets(sendline, MAXLINE, fp) == NULL) {
//eof exit
break;
}
else {
write(connfd, sendline, strlen(sendline));
}
}
}
}
编译和启动服务端
gcc selectechoserver.c -o selectechoserver
编译和启动客户端
gcc selectechoclient.c -o selectechoclient
原文：https://www.cnblogs.com/jiangzhaowei/p/8972188.html