在Linux编写C代码操作串口，网卡，音卡等设备，至少操作两种设备，给出代码

好的，下面我将分别给出Linux下C语言操作串口、网卡、音频设备的代码示例。

1. 操作串口

#include <stdio.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>

int main()
{
    int fd;
    struct termios opt;

    // 打开串口设备
    fd = open("/dev/ttyS0", O_RDWR);
    if(fd == -1)
    {
        printf("Failed to open serial port!\n");
        return -1;
    }

    // 设置串口属性
    tcgetattr(fd, &opt);
    opt.c_cflag = B115200 | CS8 | CLOCAL | CREAD;
    opt.c_iflag = IGNPAR;
    opt.c_oflag = 0;
    opt.c_lflag = 0;
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd, TCSANOW, &opt);

    // 读写串口数据
    char buf[256];
    int len;
    while(1)
    {
        len = read(fd, buf, 256);
        if(len > 0)
        {
            write(fd, buf, len);
        }
    }

    // 关闭串口设备
    close(fd);

    return 0;
}

2. 操作网卡

#include <stdio.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main()
{
    int fd;
    struct ifreq ifr;
    struct sockaddr_in *addr;

    // 创建socket
    fd = socket(AF_INET, SOCK_DGRAM, 0);
    if(fd == -1)
    {
        printf("Failed to create socket!\n");
        return -1;
    }

    // 设置网卡名称和IP地址
    strcpy(ifr.ifr_name, "eth0");
    addr = (struct sockaddr_in *)&(ifr.ifr_addr);
    addr->sin_family = AF_INET;
    addr->sin_addr.s_addr = inet_addr("192.168.1.100");
    ioctl(fd, SIOCSIFADDR, &ifr);

    // 设置网卡子网掩码
    addr->sin_addr.s_addr = inet_addr("255.255.255.0");
    ioctl(fd, SIOCSIFNETMASK, &ifr);

    // 设置网卡广播地址
    addr->sin_addr.s_addr = inet_addr("192.168.1.255");
    ioctl(fd, SIOCSIFBRDADDR, &ifr);

    // 设置网卡MAC地址
    unsigned char mac[] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55};
    memcpy(ifr.ifr_hwaddr.sa_data, mac, 6);
    ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;
    ioctl(fd, SIOCSIFHWADDR, &ifr);

    // 关闭socket
    close(fd);

    return 0;
}

3. 操作音频设备

#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>

int main()
{
    int rc;
    snd_pcm_t *handle;
    snd_pcm_hw_params_t *params;
    unsigned int val;
    int dir;
    snd_pcm_uframes_t frames;
    char *buffer;
    int size;

    // 打开PCM设备
    rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
    if(rc < 0)
    {
        printf("Failed to open PCM device!\n");
        return -1;
    }

    // 分配参数结构体
    snd_pcm_hw_params_alloca(&params);

    // 初始化参数结构体
    snd_pcm_hw_params_any(handle, params);

    // 设置参数
    snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
    snd_pcm_hw_params_set_channels(handle, params, 2);
    val = 44100;
    snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
    frames = 32;
    snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);

    // 应用参数
    rc = snd_pcm_hw_params(handle, params);
    if(rc < 0)
    {
        printf("Failed to set PCM parameters!\n");
        return -1;
    }

    // 计算缓冲区大小
    snd_pcm_hw_params_get_period_size(params, &frames, &dir);
    size = frames * 4;
    buffer = (char *)malloc(size);

    // 播放音频数据
    while(1)
    {
        // 从音频文件读取数据
        int len = fread(buffer, 1, size, stdin);
        if(len <= 0)
        {
            break;
        }

        // 写入PCM设备
        rc = snd_pcm_writei(handle, buffer, frames);
        if(rc == -EPIPE)
        {
            snd_pcm_prepare(handle);
        }
        else if(rc < 0)
        {
            printf("Failed to write PCM data!\n");
        }
    }

    // 关闭PCM设备
    snd_pcm_close(handle);
    free(buffer);

    return 0;
}

以上三段代码分别展示了如何在Linux环境下使用C语言操作串口、网卡、音频设备。