getting IntPtr of -1

[iwdu15]

hi...can anyone tell me why im getting an IntPtr of -1 being returned? the
device is plugged in and being recognized by windows....so i dont understand
this. Thanks

private void GetFiles(String str)
{

IntPtr ptrHandle;
IntPtr lpData;

short shrtInLength;
short shrtOutLength;

HidCaps oCaps;

try
{

ptrHandle = CreateFile(str, GENERIC_READ | GENERIC_WRITE, 0,
IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero);

HidD_GetPreparsedData(ptrHandle, out lpData);

HidP_GetCaps(lpData, out oCaps); // extract the device
capabilities from the internal buffer

shrtInLength = oCaps.InputReportByteLength; // get the
input...
shrtOutLength = oCaps.OutputReportByteLength; // ... and
output report lengths

//FileStream fs = new System.IO.FileStream(ptrHandle,
FileAccess.ReadWrite);

}
catch (Exception ex)
{

}
finally
{

HidD_FreePreparsedData(lpData);

}

}

--
-iwdu15

[Tom Shelton]

iwdu15 wrote:

hi...can anyone tell me why im getting an IntPtr of -1 being returned? the
device is plugged in and being recognized by windows....so i dont understand
this. Thanks

private void GetFiles(String str)
{

IntPtr ptrHandle;
IntPtr lpData;

short shrtInLength;
short shrtOutLength;

HidCaps oCaps;

try
{

ptrHandle = CreateFile(str, GENERIC_READ | GENERIC_WRITE, 0,
IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero);

HidD_GetPreparsedData(ptrHandle, out lpData);

HidP_GetCaps(lpData, out oCaps); // extract the device
capabilities from the internal buffer

shrtInLength = oCaps.InputReportByteLength; // get the
input...
shrtOutLength = oCaps.OutputReportByteLength; // ... and
output report lengths

//FileStream fs = new System.IO.FileStream(ptrHandle,
FileAccess.ReadWrite);

}
catch (Exception ex)
{

}
finally
{

HidD_FreePreparsedData(lpData);

}

}

--
-iwdu15

Can you show your actual declaration for CreateFile and the constants
your passing to it?

Thanks.

--
Tom Shelton

[Willy Denoyette [MVP]]

"iwdu15" <jmmgoalsteratyahoodotcomwrote in message
news:99**********************************@microsof t.com...
| hi...can anyone tell me why im getting an IntPtr of -1 being returned? the
| device is plugged in and being recognized by windows....so i dont
understand
| this. Thanks
|
| private void GetFiles(String str)
| {
|
| IntPtr ptrHandle;
| IntPtr lpData;
|
| short shrtInLength;
| short shrtOutLength;
|
| HidCaps oCaps;
|
| try
| {
|
| ptrHandle = CreateFile(str, GENERIC_READ | GENERIC_WRITE,
0,
| IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero);
|
| HidD_GetPreparsedData(ptrHandle, out lpData);
|
| HidP_GetCaps(lpData, out oCaps); // extract the device
| capabilities from the internal buffer
|
| shrtInLength = oCaps.InputReportByteLength; // get the
| input...
| shrtOutLength = oCaps.OutputReportByteLength; // ... and
| output report lengths
|
| //FileStream fs = new System.IO.FileStream(ptrHandle,
| FileAccess.ReadWrite);
|
| }
| catch (Exception ex)
| {
|
| }
| finally
| {
|
| HidD_FreePreparsedData(lpData);
|
| }
|
| }
|
| --
| -iwdu15

No we can't, but you can if you call Marshal.GetLastWin32Error after the
failing API call. This will return the windows error code, provided you have
declared your DllImport correctly (mind to post the declaration also??).
Note that you should always call GetLastWin32Error for API's that return
error information after the call.

Willy.

[iwdu15]

i think i figured it out...which was a big mistake on my part. i was trying
to communicate with my MP3 player, USB Device, using HID APIs....my bad,
thanks though
--
-iwdu15