前言

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

服务端

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            }        }    }

}

客户端

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));              }        }

} }

下载和编译

下载地址

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

原文地址：https://www.cnblogs.com/jiangzhaowei/p/8972188.html