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Cannot marshal string from DEV_BROADCAST_DEVICEINTERFACE in WM_DEVICECHANGE message

Hi,

I am using a C# windows app to detect insertion or removal of a USB mass storage device, and to get the USB device name when this happens.

I got as far as detecting insert/remove events, but i'm having trouble getting the device name.

I have successfully used RegisterDeviceNotification() to tell windows to send my WM_DEVICECHANGE messages for USB class devices.

When I receive a WM_DEVICECHANGE of (WParam) type DBT_DEVICEARRIVAL the MSDN docs say that LParam should point to a DEV_BROADCAST_HDR structure with some optional extra data on the end.

As I am interested in the DBT_DEVTYP_DEVICEINTERFACE structure, I check that the DEV_BROADCAST_HDR.dbch_devicetype == DBT_DEVTYP_DEVICEINTERFACE, if so then I use Marshal.PtrToStructure(...) to transfer the data in LParam to a managed struct declared as follows:

//typedef struct _DEV_BROADCAST_DEVICEINTERFACE {
// DWORD dbcc_size;
// DWORD dbcc_devicetype;
// DWORD dbcc_reserved;
// GUID dbcc_classguid;
// TCHAR dbcc_name[1];
//} DEV_BROADCAST_DEVICEINTERFACE, *PDEV_BROADCAST_DEVICEINTERFACE;
[StructLayout(LayoutKind.Sequential,CharSet = CharSet.Auto)]
internal struct DEV_BROADCAST_DEVICEINTERFACE
{
internal int dbcc_size;
internal int dbcc_devicetype;
internal int dbcc_reserved;
internal Guid dbcc_classguid;
internal string dbcc_name;
}

Soooo, here is the problem:

all the fields in my DEV_BROADCAST_DEVICEINTERFACE are populated correctly except for the one i'm after: dbcc_name.

In a sample run of my program, I plug in a USB pendrive and get the following DEV_BROADCAST_DEVICEINTERFACE data:

dbcc_size      172      int
dbcc_devicetype      5      int
dbcc_reserved      0      int
dbcc_classguid      {a5dcbf10-6530-11d2-901f-00c04fb951ed}      System.Guid
dbcc_name      ""      string

The value of 172 for dbcc_size suggests that windows IS sending the correct data, but that i'm not correctly marshalling it.

Thanks,

Ben.

pgnatyuk

This example will help you a lot:
Detecting Media Insertion or Removal
http://msdn.microsoft.com/en-us/library/aa363215(v=VS.85).aspx
(FirstDriveFromMask - pay attention on this function, this is the one character you are trying to convert to a string, but it is a mask)
DEV_BROADCAST_HDR Structure:
http://msdn.microsoft.com/en-us/library/aa363246(v=VS.85).aspx
I think you make a mistake with this structure.
Check here:
MSDN. DBT_DEVICEARRIVAL Event
http://msdn.microsoft.com/en-us/library/aa363205(v=VS.85).aspx
"If media is being inserted, the type of device arriving is a volume (the dbch_devicetype member is DBT_DEVTYP_VOLUME) and the change effects the media (the dbcv_flags member is DBTF_MEDIA)."
If I remember correctly, your app receives few such messages. Comment the code that parse this message in your app and add a Trace - you will see what's going on, no breakpoints.

ben84

ASKER

Thanks for your reply pgnatyuk, but i'm afraid what you've posted doesn't really help. I have already read all three of the above, and DBT_DEVTYP_VOLUME does not give me the info I need: the DevceID. My problem is specifically with marshalling, and I think my question should have stressed that.

ASKER CERTIFIED SOLUTION

ben84

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absingh

what is the use of the application that you are trying to build