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Detecting Media Insertion or Removal

Windows sends all top-level windows a set of default WM_DEVICECHANGE messages when new devices or media (such as a CD or DVD) are added and become available, and when existing devices or media are removed. You do not need to register to receive these default messages. See the Remarks section in RegisterDeviceNotification for details on which messages are sent by default. The messages in the code example below are among the default messages.

Each WM_DEVICECHANGE message has an associated event that describes the change, and a structure that provides detailed information about the change. The structure consists of an event-independent header, DEV_BROADCAST_HDR, followed by event-dependent members. The event-dependent members describe the device to which the event applies. To use this structure, applications must first determine the event type and the device type. Then, they can use the correct structure to take appropriate action.

When the user inserts a new CD or DVD into a drive, applications receive a WM_DEVICECHANGE message with a DBT_DEVICEARRIVAL event. The application must check the event to ensure that the type of device arriving is a volume (the dbch_devicetype member is DBT_DEVTYP_VOLUME) and that the change affects the media (the dbcv_flags member is DBTF_MEDIA).

When the user removes a CD or DVD from a drive, applications receive a WM_DEVICECHANGE message with a DBT_DEVICEREMOVECOMPLETE event. Again, the application must check the event to ensure that the device being removed is a volume and that the change affects the media.

The following code demonstrates how to check for insertion or removal of a CD or DVD.


#include <windows.h>
#include <dbt.h>
#include <strsafe.h>
#pragma comment(lib, "user32.lib" )

void Main_OnDeviceChange( HWND hwnd, WPARAM wParam, LPARAM lParam );
char FirstDriveFromMask( ULONG unitmask );  //prototype

/*------------------------------------------------------------------
   Main_OnDeviceChange( hwnd, wParam, lParam )

   Description
      Handles WM_DEVICECHANGE messages sent to the application's
      top-level window.
--------------------------------------------------------------------*/

void Main_OnDeviceChange( HWND hwnd, WPARAM wParam, LPARAM lParam )
 {
  PDEV_BROADCAST_HDR lpdb = (PDEV_BROADCAST_HDR)lParam;
  TCHAR szMsg[80];

  switch(wParam )
   {
    case DBT_DEVICEARRIVAL:
      // Check whether a CD or DVD was inserted into a drive.
      if (lpdb -> dbch_devicetype == DBT_DEVTYP_VOLUME)
       {
        PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;

        if (lpdbv -> dbcv_flags & DBTF_MEDIA)
         {
          StringCchPrintf( szMsg, sizeof(szMsg)/sizeof(szMsg[0]), 
                           TEXT("Drive %c: Media has arrived.\n"), 
                           FirstDriveFromMask(lpdbv ->dbcv_unitmask) );

          MessageBox( hwnd, szMsg, TEXT("WM_DEVICECHANGE"), MB_OK );
         }
       }
      break;

    case DBT_DEVICEREMOVECOMPLETE:
      // Check whether a CD or DVD was removed from a drive.
      if (lpdb -> dbch_devicetype == DBT_DEVTYP_VOLUME)
       {
        PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;

        if (lpdbv -> dbcv_flags & DBTF_MEDIA)
         {
          StringCchPrintf( szMsg, sizeof(szMsg)/sizeof(szMsg[0]), 
                           TEXT("Drive %c: Media was removed.\n" ),
                           FirstDriveFromMask(lpdbv ->dbcv_unitmask) );

          MessageBox( hwnd, szMsg, TEXT("WM_DEVICECHANGE" ), MB_OK );
         }
       }
      break;

    default:
      /*
        Process other WM_DEVICECHANGE notifications for other 
        devices or reasons.
      */ 
      ;
   }
}

/*------------------------------------------------------------------
   FirstDriveFromMask( unitmask )

   Description
     Finds the first valid drive letter from a mask of drive letters.
     The mask must be in the format bit 0 = A, bit 1 = B, bit 2 = C, 
     and so on. A valid drive letter is defined when the 
     corresponding bit is set to 1.

   Returns the first drive letter that was found.
--------------------------------------------------------------------*/

char FirstDriveFromMask( ULONG unitmask )
 {
  char i;

  for (i = 0; i < 26; ++i)
   {
    if (unitmask & 0x1)
      break;
    unitmask = unitmask >> 1;
   }

  return( i + 'A' );
}


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Device Events

 

 

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