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How to receive notification of CD-ROM insertion or removal

Summary
Some applications need to know when the user inserts or removes acompact disc or DVD from a CD-ROM drive without polling for media changes. Windows provide a way to notify these applications through theWM_DEVICECHANGE message. This article explains how to handle theWM_DEVICECHANGE message to detect CD-ROM or DVDmedia changes.
More information
Windows sends all top-level windows a WM_DEVICECHANGEmessage when new devices or media are added and become available, and whenexisting devices or media are removed. Each WM_DEVICECHANGE message has anevent associated with it to describe the change, and a structure thatprovides detailed information about the change.

The structure consists of an event-independent header followed by an event-dependent structure. The event-dependent part of the structure describeswhich device the event applies to. To use this structure, applications mustfirst determine the event type and the device type. Then, they can use thecorrect structure to take appropriate action.

When the user inserts a new compact disc or DVD into a drive, applications get aWM_DEVICECHANCE message with a DBT_DEVICEARRIVAL event. The applicationmust check the event to make sure that the type of device arriving is avolume (DBT_DEVTYP_VOLUME) and that the event's media flag (DBTF_MEDIA) isset.

When the user removes a compact disc from a CD-ROM drive or DVD, applications willget a WM_DEVICECHANCE message with a DBT_DEVICEREMOVECOMPLETE event. Aswith DBT_DEVICEARRIVAL above, the application must check the event to makesure that the device being removed is a volume and that the event's mediaflag is set.

Sample Code

The following code demonstrates how to use the WM_DEVICECHANGE message tocheck for compact disc or DVD insertion or removal.
   #include <windows.h>   #include <dbt.h>   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;      char szMsg[80];      switch(wParam)      {      case DBT_DEVICEARRIVAL:         // See if a CD-ROM 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)            {               wsprintf (szMsg, "Drive %c: arrived\n",                         FirstDriveFromMask(lpdbv ->dbcv_unitmask));               MessageBox (hwnd, szMsg, "WM_DEVICECHANGE", MB_OK);            }         }        break;     case DBT_DEVICEREMOVECOMPLETE:        // See if a CD-ROM 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)           {              wsprintf (szMsg, "Drive %c: was removed\n",                        FirstDriveFromMask(lpdbv ->dbcv_unitmask));              MessageBox (hwnd, szMsg, "WM_DEVICECHANGE", MB_OK);           }        }        break;     default:        /*           Other WM_DEVICECHANGE notifications get sent for other devices           or reasons; we don't care about them here.  If they were           important, we would check for them and act accordingly.        */          ;      }   }   /*----------------------------------------------------------------------   FirstDriveFromMask (unitmask)      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 3 = C, etc.      A valid drive letter is defined when the corresponding bit is set to      1.      Returns the drive letter that was first found.   ----------------------------------------------------------------------*/    char FirstDriveFromMask (ULONG unitmask)   {      char i;      for (i = 0; i < 26; ++i)      {         if (unitmask & 0x1)            break;         unitmask = unitmask >> 1;      }      return (i + 'A');   }				
Although this sample code only checks for volume arrivals due to theinsertion of new media, it can be extended to get notification of otherhardware events for other types too. To do so, you have to add cases forother device events and handle different device types for each event.
References
Microsoft Platform SDK documentation, "Device Management" overview" chapter
notify notification cdrom CD-ROM detect
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Article ID: 163503 - Last Review: 06/22/2014 18:13:00 - Revision: 6.0

Microsoft Win32 Application Programming Interface

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