Linux获取摄像头的VID及PID值

Linux中接入摄像头后会在/dev/video*中有多个描述文件，所以获取摄像头的VID及PID值还是较为有用的

• 首先找到可以捕获视频的设备

   #include <dirent.h>
   #include <libudev.h>
   #include <fstream>
   #include <pthread.h>
   #include <time.h>
   #include <vector>
   #include <unistd.h>
   #include <iostream>
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <inttypes.h>
   #include <sys/types.h>
   #include <sys/stat.h>
   #include <fcntl.h>
   #include <unistd.h>
   #include <sys/ioctl.h>
   #include <sys/mman.h>
   #include <linux/videodev2.h>//v4l2相关结构体
   #include <string.h>
  
  
  int v4l2_is_v4l_dev(const char *name)
  {
  	return !strncmp(name, "video", 5) || !strncmp(name, "radio", 5) || !strncmp(name, "vbi", 3) || !strncmp(name, "v4l-subdev", 10);
  }
  
  int main(){
      const char* dir_name = "/dev";
      DIR* dir = opendir(dir_name);
      if (!dir) {
          fprintf(stderr, "Error: couldn't open the directory: %s\n", dir_name);
          return false;
      }
  
      struct dirent* entry = nullptr;
      int fd;
  
      while ((entry = readdir(dir))) {
          if (!v4l2_is_v4l_dev(entry->d_name))
              continue;
  
          char device_name[256];
          snprintf(device_name, sizeof(device_name), "/dev/%s", entry->d_name);
          if ((fd = open(device_name, O_RDWR | O_NONBLOCK)) < 0) {
              continue;
          }
          struct v4l2_capability cap;
          if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0) {
              fprintf(stderr, "Error: cam_info: can't open device: %s\n", device_name);
                  close(fd);
                  break;
          } else {
              if(!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) || !(cap.capabilities & V4L2_CAP_STREAMING) || !(cap.capabilities & V4L2_CAP_META_CAPTURE))                 {
                  close(fd);
                  continue;
              } else {
                  printf("enable: %s\n", device_name);
                  close(fd);
              }
          }
      }
  	return 0;
  }

• 获取vid及pid

  #define udev_list_entry_foreach(entry, first) \
       for (entry = first; \
            entry != NULL; \
            entry = udev_list_entry_get_next(entry))
   
   typedef struct {
       string vid;
       string pid;
   } VPID;
   
   bool read_vpid(string dev_path, VPID& vpid)
   {
       bool success = false;
   
       auto udev = udev_new();
       if (!udev) {
           return false;
       }
   
       struct stat statbuf;
       if (stat(dev_path.c_str(), &statbuf) < 0) {
           return false;
       }
   
       auto type =  S_ISBLK(statbuf.st_mode) ? 'b' : S_ISCHR(statbuf.st_mode) ? 'c' : 0;
   
       auto opened_dev = udev_device_new_from_devnum(udev, type, statbuf.st_rdev);
       auto dev = opened_dev;
   
       struct udev_list_entry *list_entry;
       udev_list_entry_foreach(list_entry, udev_device_get_properties_list_entry(dev))
       {
           success = true;
           if(strcmp(udev_list_entry_get_name(list_entry), "ID_VENDOR_ID") == 0)
               vpid.vid = udev_device_get_property_value(dev, udev_list_entry_get_name(list_entry));
   
           if(strcmp(udev_list_entry_get_name(list_entry), "ID_MODEL_ID") == 0)
               vpid.pid = udev_device_get_property_value(dev, udev_list_entry_get_name(list_entry));
   
           //printf("==== vid: %s\n pid: %s\n", vpid.vid.c_str(), vpid.pid.c_str());
           //printf("%s=%s\n", udev_list_entry_get_name(list_entry), udev_list_entry_get_value(list_entry));
       }
       printf("\n");
       if (opened_dev) {
           udev_device_unref(opened_dev);
       }
       udev_unref(udev);
   
       return success;
   }
  
  # 根据vid、pid可区分具体的摄像头

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