函数select、poll

函数select

select函数：

int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

参数：

nfds：监控的文件描述符集里最大文件描述符加1，因为此参数会告诉内核检测前多少个文件文件描述符
readfs：监控有读数据到达文件描述符集合，传入传出参数
writefds：监控写数据到达文件描述符集合，传入传出参数
exceptfds：监控异常发生到达文件描述符集合，如带外数据到达异常，传入传出参数
timeout：定时阻塞监控时间。

void FD_CLR(int fd, fd_set *set);     // 把文件描述符集里fd位清0
int  FD_ISSET(int fd, fd_set *set);   // 测试文件描述符集里fd是否置1
void FD_SET(int fd, fd_set *set);     // 把文件描述符集合里fd位置1
void FD_ZERO(fd_set *set);            // 把文件描述符集合里所有位清0

1. 测试代码：

服务端

 1 //server.c
 2 #include <unistd.h>
 3 #include <stdio.h>
 4 #include <string.h>
 5 #include <netinet/in.h>
 6 #include <arpa/inet.h>
 7 #include <signal.h>
 8 #include <sys/wait.h>
 9 #include <ctype.h>
10 #include <unistd.h>
11 #include <sys/select.h>
12 #include "wrap.h"
13  
14 #define SERV_PROT 6666
15  
16 int main(int argc, char *argv[])
17 {
18     int i, j, n, nread;
19  
20     int maxfd = 0;
21     int listenfd, connfd;
22     char buf[BUFSIZ];
23  
24     struct sockaddr_in clie_addr, serv_addr;
25     socklen_t clie_addr_len;
26     listenfd = Socket(AF_INET, SOCK_STREAM, 0);
27  
28     int opt = 1;
29     setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
30  
31     bzero(&serv_addr, sizeof(serv_addr));
32     serv_addr.sin_family = AF_INET;
33     serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
34     serv_addr.sin_port = htons(SERV_PROT);
35     Bind(listen, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
36     Listen(listenfd, 128);
37  
38     fd_set rset, allset;
39     maxfd = listenfd;
40     FD_ZERO(&allset);
41     FD_SET(listenfd, &allset);
42     while (1)
43     {
44         rset = allset;
45         nread = select(maxfd + 1, &rset, NULL, NULL, NULL);  //每次循环都从新设置select监控信号集
46         if(nread < 0)
47             perr_exit("select error");
48  
49         if (FD_ISSET(listenfd, &rset))   //说明有新的客户端连接请求
50         {
51             clie_addr_len = sizeof(clie_addr);
52             connfd = Accept(listenfd, (struct sockaddr *)&clie_addr, &clie_addr_len);
53  
54             FD_SET(connfd, &allset); //向监控文件描述符集合allset添加新的文件描述符connfd
55  
56             if (maxfd < connfd)
57                 maxfd = connfd;
58  
59             if (0 == --nread)  //说明select只返回一个，并且listenfd，后续执行无须执行
60                 continue;
61         }
62         for (i = listenfd + 1; i <= maxfd; i++)
63         {
64             if (FD_ISSET(i, &rset))
65             {
66                 if ((n = Read(i, buf, sizeof(buf))) == 0)  //当client关闭链接时， 服务端也关闭对应链接
67                 {
68                     Close(i);
69                     FD_CLR(i, &allset);  //解除select对此文件描述符的监控
70                 }
71                 else if(n == -1)
72                     perr_exit("read error");
73                 for (j = 0; j < n; ++j)
74                     buf[j] = toupper(buf[j]);
75                 Write(i, buf, n);
76             }
77         }
78     }
79     Close(listenfd);
80     return 0;
81 }

View Code

客户端

 1 //client.c
 2 #include <arpa/inet.h>
 3 #include "wrap.h"
 4  
 5 #define SERV_IP "192.168.245.139"
 6 #define SERV_PORT 6666
 7  
 8 int main(void)
 9 {
10     int sfd, len;
11     struct sockaddr_in serv_addr;
12     char buf[BUFSIZ];
13     sfd = Socket(AF_INET, SOCK_STREAM, 0);
14     bzero(&serv_addr, sizeof(serv_addr));
15     serv_addr.sin_family = AF_INET;
16     inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr.s_addr);
17     serv_addr.sin_port = htons(SERV_PORT);
18     Connect(sfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
19  
20     while (1) 
21     {
22         fgets(buf, sizeof(buf), stdin);
23         int r = Write(sfd, buf, strlen(buf));
24         printf("Write r ======== %d
", r);
25         len = Read(sfd, buf, sizeof(buf));
26         printf("Read len ========= %d
", len);
27         Write(STDOUT_FILENO, buf, len);
28     }
29     Close(sfd);
30     return 0;
31 }

View Code

代码下载地址：链接

输出结果：