Monitor terminal input with Select

First, a description of the Select function is found in the Man Manual, as follows:

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

which
Nfds: Refers to the range of all file descriptors in the collection, that is, the maximum value of all file descriptors plus 1
Readfds/writefds: The monitoring file read (write) attribute, the collection has a file readable (write), the return value is greater than 0, otherwise, according to timeout to determine whether to timeout, if time-out, the return value is 0 If an error occurs, return-1. If the value is null, the read (write) property of the file in the collection is not cared for.
Exceptfds: Monitoring file Exception Errors
Timeout: You can have the select in three states:
1. NULL: Block until a file in the file descriptor collection has changed;
2.0s 0ms: non-blocking, regardless of the file descriptor changes, immediately return to continue execution, the file returns 0 without changes, there is a change to return a positive value;
3. Greater than 0: blocked in timeout time, the timeout period has the arrival of the event returned, otherwise after the timeout, anyway must return, the return value with the above.

Select: Monitor FD set changes
FD_CLR Delete an FD in the FD collection
Fd_isset tests whether an FD in the FD collection can read and write
Fd_set adding FD to the FD collection
Fd_zero emptying the FD collection

0:stdin 1:stdout 2:stderr

With the above description of SELECT, the following procedure is attached:

1#include <stdio.h>2#include <stdlib.h>3#include <sys/time.h>4#include <sys/types.h>5#include <unistd.h>6 7 8 #defineSTDIN 09 Ten intMain () One { A     //1. Initializing the FD collection -Fd_set FDS;//defining an FD collection -Fd_zero (&fds);//emptying the FD collection theFd_set (Stdin,&fds);//Add stdin -     //2. Monitoring FD Set-Traversal collection mode -     intRET =Select(stdin+1,&fds,null,null,null); -     if(ret = =-1) +     { -Perror ("Select"); +Exit1); A     } at      -     //3. Determine if the read attribute of the stdin has changed -     if(Fd_isset (stdin,&FDS)) -printf"someone input a char!\n"); -      -     //4. Emptying the collection inFD_CLR (stdin,&FDS); -Fd_zero (&FDS); to     return 0; +}

Monitor terminal input with Select