Open a /dev device and grab data with v4l

c-programming programming snippet

#include <linux/videodev2.h>
#include <libv4l2.h>
#include <glib.h>
#include <fcntl.h>
#include <sys/ioctl.h>


enumerate = udev_enumerate_new(udev);
udev_enumerate_add_match_subsystem(enumerate, "video4linux");
udev_enumerate_scan_devices(enumerate);
devices = udev_enumerate_get_list_entry(enumerate);
/* For each item enumerated, print out its information.
   udev_list_entry_foreach is a macro which expands to
   a loop. The loop will be executed for each member in
   devices, setting dev_list_entry to a list entry
   which contains the device's path in /sys. */
udev_list_entry_foreach(dev_list_entry, devices)
{
   const char *path;

   /* Get the filename of the /sys entry for the device
and create a udev_device object (dev) representing it */
   path = udev_list_entry_get_name(dev_list_entry);
   dev = udev_device_new_from_syspath(udev, path);
   std::cout << "DEV: " << dev << std::endl;
   std::cout << "PATH: " << *path << std::endl;

   /* usb_device_get_devnode() returns the path to the device node
itself in /dev. */
   const gchar *v4l2_device = udev_device_get_devnode(dev);

   /* open the device and query the capabilities */
   if ((fd = v4l2_open(v4l2_device, O_RDWR | O_NONBLOCK, 0)) < 0)
   {
      g_printerr("ERROR opening V4L2 interface for %s\n", v4l2_device);
      v4l2_close(fd);
      continue; /*next dir entry*/
   }

   if (xioctl(fd, VIDIOC_QUERYCAP, &v4l2_cap) < 0)
   {
      perror("VIDIOC_QUERYCAP error");
      g_printerr("   couldn't query device %s\n", v4l2_device);
      v4l2_close(fd);
      continue; /*next dir entry*/
   }
   v4l2_close(fd);

   }