linux下使用poll读取terminal终端上等待回车后送入的一行字符串

《linux下如何从terminal终端tcsetattr立即得到输入字符，而不等待回车键》
/*
 * Copyright (c) 2009 Luther Ge
 */
#include
#include
#include

int main(void)
{
    struct pollfd pfds;
    int retval;
    char str[256];

    memset(&pfds, 0, sizeof(pfds));
    pfds.fd = 0;
    pfds.events = POLLIN;

    retval = poll(&pfds, 1, 2*1000);

    if (pfds.revents & POLLIN) {
        fscanf(stdin, "%s", str);
        printf("=========\ninput string is : %s\n", str);
    } else {
        printf("timeout : %d, %x\n", retval, pfds.revents);
    }
}

luther@gliethttp:/vobs/tmp$ ./a.out
HelloWorld!
=========
input string is : HelloWorld!
luther@gliethttp:/vobs/tmp$ ./a.out
timeout : 0, 0
luther@gliethttp:/vobs/tmp$