使用select函数循环读取键盘输入

#include <sys/time.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <sys/select.h>
int main()
{
    int keyboard;
    int ret,i;
    char c;
    fd_set readfd;
    struct timeval timeout;
    //非阻塞地读取终端上的输入信息，/dev/tty当前终端
    keyboard=open("/dev/tty",O_RDONLY | O_NONBLOCK);
    //如果条件返回错误，则终止程序执行
    assert(keyboard>0);
    while(1)
    {
        timeout.tv_sec=5;//超时时间设置为5s
        timeout.tv_usec=0;
        FD_ZERO(&readfd);   //清空可读的fd集合
        //把打开终端的fd加入到可读fd集合中
        FD_SET(keyboard,&readfd);
        //调用select查看是否有可读的fd
        ret=select(keyboard+1, &readfd, NULL, NULL, &timeout);
        
        //表示调用select失败
        if(ret==-1)
            perror("select error");
       else if(ret)
       {
            //判断终端的fd是否在可读描述符集合中
        if(FD_ISSET(keyboard,&readfd))
        {
            i=read(keyboard, &c, 1);
            if(c=='\n')
                continue;
            printf("The input is %c\n",c);
            if(c=='q')
                break;
        }
       }

       //表示等待时间超时
       else if(ret==0)
        printf("time out\n");
    }
    return 0;
}