观察select超时的表现

 1 #include <sys/time.h>
 2 #include <stdio.h>
 3 #include <sys/types.h>
 4 #include <sys/stat.h>
 5 #include <fcntl.h>
 6 #include <assert.h>
 7 #include <stdlib.h>
 8 #include <string.h>
 9 #include <unistd.h>
10 #include <sys/socket.h>
11 #include <netinet/in.h>
12 #include <arpa/inet.h>
13 #include <errno.h>
14 #include <sys/select.h>
15 
16 int main()
17 {
18     int keyboard;
19     int ret,i;
20     char c;
21     fd_set readfd;
22     struct timeval timeout;
23     keyboard = open("/dev/tty",O_RDONLY|O_NONBLOCK);
24     assert(keyboard>0);
25     while(1){
26         timeout.tv_sec = 5;
27         timeout.tv_usec = 0;
28         FD_ZERO(&readfd);
29         FD_SET(keyboard,&readfd);
30         ret = select(keyboard+1,&readfd,NULL,NULL,&timeout);
31         if(ret == -1){
32             perror("select error!\n");
33         }
34         else if(ret){
35             if(FD_ISSET(keyboard,&readfd)){
36                 i = read(keyboard,&c,1);
37                 if(‘\n‘==c)
38                     continue;
39                 printf("The input is %c\n",c);
40                 if(‘q‘==c)
41                     break;
42             }
43         }
44         else if(ret == 0){
45             printf("time out !\n");
46         }
47     }
48     return 0;
49 }