#include <iostream>
#include <poll.h>
#include <stdio.h>
#include <unistd.h>

#include <fcntl.h>
#include <errno.h>
#include <cmath>
#include <string.h>

#include <sys/types.h>
#include <sys/stat.h>

using namespace std;

int main()
{
    cout << "Hello World!" << endl;

    int ret;
    int fd;
    struct pollfd fds[2];
    char tempp[100] = {0};

    fd = open("./data.txt", O_RDONLY);
    if(fd < 0) {
        perror("open file: ");
        return -1;
    }


    ret = 0;
    fds[0].fd = 0;
    fds[1].fd = fd;

    fds[0].events = POLLIN;
    fds[1].events = POLLIN;

    while (1) {
        ret = poll(fds, 2, -1);

        if(ret == -1)
            perror("poll(): ");
        else if(ret > 0){
            char buf[100] = {0};
            if((fds[0].revents & POLLIN) == POLLIN) {
                read(0, buf, sizeof(buf));
                printf("stdin buf = %s\n", buf);
            } else if((fds[1].revents & POLLIN) == POLLIN) {
                lseek(fd, 0, SEEK_SET);
                read(fd, buf, sizeof(buf));
                if(strcmp(buf, tempp) != 0) {
                    memcpy(tempp, buf, sizeof(buf));
                    printf("file buf = %s tempp = %s\n", buf, tempp);
                }
        } else if(ret == 0)
            printf("time out\n");

        sleep(1);
    }

    return 0;
}

测试方法：

        通过lseek将每次读取文件都移到文件开头的位置。