将从摄像头获取的MJPEG数据，通过调用zbar库实现扫描二维码的功能，需要申请4个缓冲帧， 并且不得使用opencv的接口， 请写出C程序

好的，下面是一个简单的C程序，可以实现从摄像头获取MJPEG数据，调用zbar库实现扫描二维码的功能，同时申请4个缓冲帧，不使用OpenCV接口。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <zbar.h>

#define BUFFER_NUM 4

struct buffer
{
    void *start;
    size_t length;
};

int fd;
struct buffer buffers[BUFFER_NUM];
zbar_image_scanner_t *scanner;

int xioctl(int fd, int request, void *arg)
{
    int r;

    do {
        r = ioctl(fd, request, arg);
    } while (-1 == r && EINTR == errno);

    return r;
}

void process_image(const void *p, int size)
{
    zbar_image_t *image = zbar_image_create();
    zbar_image_set_format(image, *(unsigned long *)"YUYV");
    zbar_image_set_size(image, 640, 480); // 设置分辨率为640x480
    zbar_image_set_data(image, p, size, NULL);

    // 扫描二维码
    zbar_scan_image(scanner, image);

    const zbar_symbol_t *symbol = zbar_image_first_symbol(image);
    while (symbol != NULL) {
        // 输出二维码内容
        printf("Decode QR Code: %s\n", zbar_symbol_get_data(symbol));
        symbol = zbar_symbol_next(symbol);
    }

    zbar_image_destroy(image);
}

int main(int argc, char *argv[])
{
    fd = open("/dev/video0", O_RDWR);
    if (fd < 0) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    struct v4l2_capability cap;
    if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
        perror("VIDIOC_QUERYCAP");
        exit(EXIT_FAILURE);
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
        fprintf(stderr, "not a video capture device\n");
        exit(EXIT_FAILURE);
    }

    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
        fprintf(stderr, "does not support streaming i/o\n");
        exit(EXIT_FAILURE);
    }

    struct v4l2_format fmt;
    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = 640;
    fmt.fmt.pix.height = 480;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_ANY;
    if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) {
        perror("VIDIOC_S_FMT");
        exit(EXIT_FAILURE);
    }

    // 申请缓冲帧
    struct v4l2_requestbuffers req;
    memset(&req, 0, sizeof(req));
    req.count = BUFFER_NUM;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
        perror("VIDIOC_REQBUFS");
        exit(EXIT_FAILURE);
    }

    for (int i = 0; i < BUFFER_NUM; i++) {
        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf)) {
            perror("VIDIOC_QUERYBUF");
            exit(EXIT_FAILURE);
        }

        buffers[i].length = buf.length;
        buffers[i].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
        if (MAP_FAILED == buffers[i].start) {
            perror("mmap");
            exit(EXIT_FAILURE);
        }
    }

    // 初始化zbar库
    zbar_set_verbosity(0);
    scanner = zbar_image_scanner_create();
    zbar_image_scanner_set_config(scanner, 0, ZBAR_CFG_ENABLE, 1);

    // 开始采集数据
    for (int i = 0; i < BUFFER_NUM; i++) {
        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
            perror("VIDIOC_QBUF");
            exit(EXIT_FAILURE);
        }
    }

    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)) {
        perror("VIDIOC_STREAMON");
        exit(EXIT_FAILURE);
    }

    while (1) {
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(fd, &fds);

        struct timeval tv;
        tv.tv_sec = 2;
        tv.tv_usec = 0;

        int r = select(fd+1, &fds, NULL, NULL, &tv);
        if (-1 == r) {
            if (EINTR == errno) {
                continue;
            }
            perror("select");
            exit(EXIT_FAILURE);
        }
        if (0 == r) {
            fprintf(stderr, "select timeout\n");
            exit(EXIT_FAILURE);
        }

        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
            perror("VIDIOC_DQBUF");
            exit(EXIT_FAILURE);
        }

        process_image(buffers[buf.index].start, buf.bytesused);

        if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) {
            perror("VIDIOC_QBUF");
            exit(EXIT_FAILURE);
        }
    }

    for (int i = 0; i < BUFFER_NUM; i++) {
        munmap(buffers[i].start, buffers[i].length);
    }

    zbar_image_scanner_destroy(scanner);

    close(fd);

    return 0;
}

这个程序可以从/dev/video0设备获取MJPEG数据，并使用zbar库实现扫描二维码的功能。程序中申请了4个缓冲帧，并使用了Linux V4L2接口来进行视频采集、缓冲帧管理等操作。请注意，程序中使用的是YUYV格式的视频数据，如果你的摄像头输出的是其他格式的数据，需要修改程序中的格式设置。