select_tcp

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/*select_tcp.c*/

#include<stdlib.h>

#include<stdio.h>

#include<errno.h>

#include<string.h>

#include<netdb.h>

#include<sys/types.h>

#include<netinet/in.h>

#include<sys/socket.h>

#include<sys/time.h>

#include<sys/ioctl.h>

#define portnumber 3333

int main()

{

int server_sockfd,client_sockfd;

int server_len,client_len;

struct sockaddr_in server_address;

struct sockaddr_in client_address;

int result;

fd_set readfds,testfds;

/*为服务器创建并命名一个套接字*/

server_sockfd=socket(AF_INET,SOCK_STREAM,0);

server_address.sin_family=AF_INET;

server_address.sin_addr.s_addr=htonl(INADDR_ANY);

server_address.sin_port=htons(portnumber);

server_len=sizeof(server_address);

bind(server_sockfd,(struct sockaddr *)&server_address,server_len);

/*创建一个接连队列，初始化readfds以处理来自server_sockfd的输入*/

listen(server_sockfd,5);

FD_ZERO(&readfds);

FD_SET(server_sockfd,&readfds);

while(1)

{

char ch;

int fd;

int nread;

testfds=readfds;

printf("server waiting\n");

result=select(FD_SETSIZE,&testfds,(fd_set *)0,(fd_set *)0,(struct timeval *)0);

if(result<1)

{

perror("server");

exit(1);

}

/*一旦得知有活动发生，可以用FD_ISSET来依次检查每个描述符，以发现活动发生在哪个描述符上*/

for(fd=0;fd<FD_SETSIZE;fd++)

{

if(FD_ISSET(fd,&testfds))

/*如果活动发生在套接字server_sockfd上，肯定是一个新的连接请求,就可以把client_sockfd添加到描述符集合中*/

{

if(fd==server_sockfd)

{

client_len=sizeof(client_address);

client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,&client_len);

FD_SET(client_sockfd,&readfds);

printf("adding client on fd %d\n",client_sockfd);

}

/*如果活动不是发生在服务器套接字上，那肯定是客户的活动*/

else

{

ioctl(fd,FIONREAD,&nread);

if(nread==0)

{

close(fd);

FD_CLR(fd,&readfds);

printf("removing client on fd %d\n",fd);

}

else

{

read(fd,&ch,1);

sleep(2);

printf("serveing client on fd %d\n",fd);

ch++;

write(fd,&ch,1);

}