常用的USB拍照功能代碼：


#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <linux/types.h>
#include <linux/videodev2.h>
#include <malloc.h>
#include <math.h>
#include <string.h>
#include <sys/mman.h>
#include <errno.h>
#include <assert.h>
#include<QDebug>
#include<QUuid>
#include<QDir>
#include<QDateTime>
#include "uvcTest.h"
#define FILE_VIDEO  "/dev/video0"
#define JPG "./image%d.jpg"
BUFTYPE *usr_buf;
static unsigned int n_buffer = 0;
//set video capture ways(mmap)
int init_mmap(int fd)
{
    //to request frame cache, contain requested counts
    struct v4l2_requestbuffers reqbufs;
    //request V4L2 driver allocation video cache
    //this cache is locate in kernel and need mmap mapping
    memset(&reqbufs, 0, sizeof(reqbufs));
    reqbufs.count = 4;
    reqbufs.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbufs.memory = V4L2_MEMORY_MMAP;
    if(-1 == ioctl(fd,VIDIOC_REQBUFS,&reqbufs)){
        perror("Fail to ioctl ‘VIDIOC_REQBUFS‘");
        exit(EXIT_FAILURE);
    }
    n_buffer = reqbufs.count;
    printf("n_buffer = %d\n", n_buffer);
//    usr_buf = (BUFTYPE *)calloc(reqbufs.count, sizeof(usr_buf));
    usr_buf = new BUFTYPE[reqbufs.count*sizeof(BUFTYPE)];
    if(usr_buf == NULL){
        printf("Out of memory\n");
        exit(-1);
    }
    //map kernel cache to user process
    for(n_buffer = 0; n_buffer < reqbufs.count; ++n_buffer){
        //stand for a frame
        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffer;
        //check the information of the kernel cache requested
        if(-1 == ioctl(fd,VIDIOC_QUERYBUF,&buf))
        {
            perror("Fail to ioctl : VIDIOC_QUERYBUF");
            exit(EXIT_FAILURE);
        }
        usr_buf[n_buffer].length = buf.length;
        usr_buf[n_buffer].start =
            (char *)mmap(
                    NULL,
                    buf.length,
                    PROT_READ | PROT_WRITE,
                    MAP_PRIVATE,
                    fd,
                    buf.m.offset
                );
        if(MAP_FAILED == usr_buf[n_buffer].start)
        {
            perror("Fail to mmap");
            exit(EXIT_FAILURE);
        }
    }
    return 0;
}
//initial camera device
int init_camera_device(int fd)
{
    //decive fuction, such as video input
    struct v4l2_capability cap;
    //video standard,such as PAL,NTSC
    struct v4l2_standard std;
    //frame format
    struct v4l2_format tv_fmt;
    //check control
    struct v4l2_queryctrl query;
    //detail control value
    struct v4l2_fmtdesc fmt;
    int ret;
    //get the format of video supply
    memset(&fmt, 0, sizeof(fmt));
    fmt.index = 0;
    //supply to image capture
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    // show all format of supply
    printf("Support format:\n");
    while(ioctl(fd, VIDIOC_ENUM_FMT, &fmt) == 0){
        fmt.index++;
        printf("pixelformat = ‘‘%c%c%c%c‘‘\ndescription = ‘‘%s‘‘\n",fmt.pixelformat & 0xFF, (fmt.pixelformat >> 8) & 0xFF,(fmt.pixelformat >> 16) & 0xFF, (fmt.pixelformat >> 24) & 0xFF,fmt.description);
    }
    //check video decive driver capability
    ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
    if(ret < 0){
        perror("Fail to ioctl VIDEO_QUERYCAP");
        exit(EXIT_FAILURE);
    }
    //judge wherher or not to be a video-get device
    if(!(cap.capabilities & V4L2_BUF_TYPE_VIDEO_CAPTURE))
    {
        printf("The Current device is not a video capture device\n");
        exit(-1);
    }
    //judge whether or not to supply the form of video stream
    if(!(cap.capabilities & V4L2_CAP_STREAMING))
    {
        printf("The Current device does not support streaming i/o\n");
        exit(EXIT_FAILURE);
    }
    //set the form of camera capture data
    tv_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    tv_fmt.fmt.pix.width = 100;
    tv_fmt.fmt.pix.height = 100;
    tv_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
    tv_fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
    if (ioctl(fd, VIDIOC_S_FMT, &tv_fmt)< 0) {
        printf("VIDIOC_S_FMT\n");
        exit(-1);
        close(fd);
    }
    //initial video capture way(mmap)
    init_mmap(fd);
    return 0;
}
int open_camera_device(const char *dev_name)
{
    int fd;
    QString devName =QString(QLatin1String(dev_name));
    QString strDevName = QString("sudo chmod 777 %1").arg(devName);
    qDebug()<<"strDevName"<<strDevName;
//    system(strDevName.toStdString().c_str());
    //open video device with block
    fd = open(FILE_VIDEO, O_RDONLY);
    if(fd < 0){
        perror(FILE_VIDEO);
        exit(EXIT_FAILURE);
    }
    return fd;
}
int start_capture(int fd)
{
    unsigned int i;
    enum v4l2_buf_type type;
    //place the kernel cache to a queue
    for(i = 0; i < n_buffer; 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 == ioctl(fd, VIDIOC_QBUF, &buf)){
            perror("Fail to ioctl ‘VIDIOC_QBUF‘");
            exit(EXIT_FAILURE);
        }
    }
    //start capture data
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if(-1 == ioctl(fd, VIDIOC_STREAMON, &type)){
        printf("i=%d.\n", i);
        perror("VIDIOC_STREAMON");
        close(fd);
        exit(EXIT_FAILURE);
    }
    return 0;
}
int process_image(void *addr, int length, int count, char *workOrder)
{
    FILE *fp;
    count = 0;
//    static int num = 0;
//    char image_name[20];
    char* image_name;
    QUuid id = QUuid::createUuid();
    QString strId = id.toString();
    strId.append(".jpeg");
//    QString timeName = QDateTime::currentDateTime().toString("yyyyMMddhhmmss");
    QString timeName = QString(QLatin1String(workOrder));
    QDir dir("./photo");
    if(!dir.exists())
        dir.mkdir((dir.currentPath()+"/photo"));
    timeName.append(".jpeg");
//    sprintf(image_name, JPG, count++);
//    strId.toLatin1();
    QByteArray ba = timeName.toLatin1();
    image_name=ba.data();
    if((fp = fopen(image_name, "wb")) == NULL){
        perror("Fail to fopen");
        exit(EXIT_FAILURE);
    }
    fwrite(addr, length, 1, fp);
    usleep(500);
    fclose(fp);
    return 0;
}
int read_frame(int fd,char *workOrder)
{
    struct v4l2_buffer buf;
    unsigned int i;
    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    //put cache from queue
    if(-1 == ioctl(fd, VIDIOC_DQBUF,&buf)){
        perror("Fail to ioctl ‘VIDIOC_DQBUF‘");
        exit(EXIT_FAILURE);
    }
    assert(buf.index < n_buffer);
    //read process space‘s data to a file
    process_image(usr_buf[buf.index].start, usr_buf[buf.index].length,buf.index,workOrder);
//    qDebug()<<QString((char*)usr_buf[buf.index].start);
    if(-1 == ioctl(fd, VIDIOC_QBUF,&buf)){
        perror("Fail to ioctl ‘VIDIOC_QBUF‘");
        exit(EXIT_FAILURE);
    }
    return 1;
}
/**
 * @brief mainloop
 * @param fd        文件描述符
 * @param count     拍攝的圖片張數
 * @return
 */
int mainloop(int fd, int count, char *workOrder)
{
//    int count = 10;
    while(count-- > 0)
    {
        for(;;)
        {
            fd_set fds;
            struct timeval tv;
            int r;
            FD_ZERO(&fds);
            FD_SET(fd,&fds);
            /*Timeout*/
            tv.tv_sec = 2;
            tv.tv_usec = 0;
            r = select(fd + 1,&fds,NULL,NULL,&tv);
            if(-1 == r)
            {
                if(EINTR == errno)
                    continue;
                perror("Fail to select");
                exit(EXIT_FAILURE);
            }
            if(0 == r)
            {
                fprintf(stderr,"select Timeout\n");
                exit(-1);
            }
            if(read_frame(fd,workOrder))
                break;
        }
    }
    return 0;
}
void stop_capture(int fd)
{
    enum v4l2_buf_type type;
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if(-1 == ioctl(fd,VIDIOC_STREAMOFF,&type))
    {
        qDebug()<<"stop"<<fd;
        perror("Fail to ioctl ‘VIDIOC_STREAMOFF‘");
        exit(EXIT_FAILURE);
    }
    return;
}
void close_camera_device(int fd)
{
    unsigned int i;
    for(i = 0;i < n_buffer; i++)
    {
        if(-1 == munmap(usr_buf[i].start,usr_buf[i].length)){
            exit(-1);
        }
    }
    delete[] usr_buf;
//    qDebug()<<"closedf"<<fd;
    if(-1 == close(fd))
    {
        qDebug()<<"close"<<fd;
        perror("Fail to close fd");
        exit(EXIT_FAILURE);
    }
    return;
}

本文出自 “7959904” 博客，請務必保留此出處http://7969904.blog.51cto.com/7959904/1931827

USB拍照功能