如何在C++中无阻塞地从USB设备轮询数据？

问题背景 #

我有一台通过USB连接的设备，每隔几秒会输出以换行符分隔的字符流。我需要实现重复轮询该设备获取输入，且无输入时不会阻塞。尝试使用poll()函数但无法正常运行，排查困难。设备路径为/dev/ttyACM0，执行cat /dev/ttyACM0命令可以正常看到数据流。

最初触发段错误的程序 #

#include <iostream>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <poll.h>
#include <unistd.h>

int main (int argc, char* argv[]){
    char buf[1024];
    int fd = open("/dev/ttyACM0", O_RDONLY | O_NONBLOCK);
    int ret;
    if (fd < 0){
        std::cout << "ERROR" << fd << std::endl;
    }

    int i;

    struct pollfd *pfds;

    while(1){
        pfds->fd = 0;
        pfds->events = POLLIN;
        ret = poll(pfds, 1, 0);
        if (ret > 0) {
            if (pfds->revents & POLLWRBAND)
            {
                i = read(0, buf, 1024);
                if (!i){
                    printf("stdin closed\n");
                    return 0;
                }
                std::cout << i << std::endl;
            }
        }
    }

    return 0;
}

修复后的可用版本 #

#include <poll.h>
#include <iostream>
#include <cstring>
#include <fcntl.h>
#include <unistd.h>


int main(){

    char readBuf[5];
    char c;
    std::string buf;
    int counter = 0;
    int ret;
    int i;

    struct pollfd mypoll;
    int fd = open("/dev/ttyACM0", O_RDONLY | O_NONBLOCK);

    //init mypoll
    memset(&mypoll, 0, sizeof(mypoll));
    mypoll.fd = fd;
    mypoll.events = POLLIN;

    while(1){
        // poll (pointer to pollfd, number of polls, timeout)
        // noneg = successful poll
        // 0 = systemcall timeout (no data)
        // -1, errno set to indicate error
        ret = poll(&mypoll, 1, 0);
        if (ret == 1){
            int bytes_read = read(fd, readBuf, sizeof(readBuf));
            for (i = 0; readBuf[i] != '\n' && i < bytes_read; i++){
                buf.push_back(readBuf[i]);
            }
            std::cout << "#" << buf << "#" << std::endl;
            buf = "";   
        }
    }

    printf("done\n");

    close(fd);

    return 0; 
}

内容的提问来源于stack exchange，提问作者user19802847