V4L2摄像头获取单张图片

#include 
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#define CLEAR(x) memset (&(x),0,sizeof(x))

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

static char * dev_name ="/dev/video0";
static int fd = -1;
struct buffer * buffers = NULL;
FILE *file_fd;
static unsigned long file_length;
static unsigned char * file_name;

int main(int argc,char **argv)
{
    struct v4l2_capability cap;
    struct v4l2_format fmt;

    file_fd = fopen("psb.jpg","w");

    fd = open( dev_name,O_RDWR | O_NONBLOCK,0);

    ioctl(fd,VIDIOC_QUERYCAP,&cap);

    CLEAR(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_INTERLACED;
    ioctl(fd,VIDIOC_S_FMT,&fmt);

    file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;

    buffers = calloc(1,sizeof(*buffers));

    buffers[0].length = file_length;
    buffers[0].start = malloc(file_length);

    for(;;)
    {
        fd_set fds;

        struct timeval tv;
        int r;
        FD_ZERO(&fds);

        FD_SET(fd,&fds);

        tv.tv_sec = 3;
        tv.tv_usec = 0;
        r = select(fd+1,&fds,NULL,NULL,&tv);

        if(-1 == r)
        {
            if(EINTR == errno)
                continue;
            printf("select");
        }

        if(0 == r)
        {
            fprintf(stderr,"select timeout\n");
            exit(EXIT_FAILURE);
        }

        if(read(fd,buffers[0].start,buffers[0].length))
            break;
    }
    fwrite(buffers[0].start,buffers[0].length,1,file_fd);
    free(buffers[0].start);

    close(fd);
    fclose(file_fd);
    exit(EXIT_SUCCESS);
    return 0;
}