Calling unmanaged DLL issue

[Sid Price]

Hello,
I am trying to call an unmanaged API (IP helper) and having problems getting
started. I have the following code to read an IP Forward table. It appears
my first call to "GetIPForwardTa ble" appears to work, it returns the
required buffer size in the ByteCount variable. However when I try the
second call, the one that should actually read the table the application
simply exits. This suggests a stack corruption or similar. Can anyone see
what is wrong with the code?
Dim lpDataBuffer As IntPtr

Dim BufferSize As Int32

Dim ByteCount As Int32 = Marshal.SizeOf( BufferSize)

Dim Result As Int32

'

' create unmanged data buffer that is too small for real data,

' this will force the method to return the actual byte count needed

'

lpDataBuffer = Marshal.AllocHG lobal(2)

Try

'

' First do a read, the buffer size is too small, this

' will return the needed size in the buffer size buffer

'

Result = GetIpForwardTab le(lpDataBuffer , ByteCount, True)

'

' Free the unmanged data buffer

'

Marshal.FreeHGl obal(lpDataBuff er)

'

' Create a new buffer for the real data

'

lpDataBuffer = Marshal.AllocHG lobal(5000)

'

' Read the table

'

Result = GetIpForwardTab le(lpDataBuffer , ByteCount, True)

Catch ex As Exception

MsgBox("OOPS!")

End Try



Thanks for any pointers,

Sid.

[Tom Shelton]

Re: Calling unmanaged DLL issue

On 2008-05-02, Sid Price <sid@nowhere.co mwrote:

Hello,
I am trying to call an unmanaged API (IP helper) and having problems getting
started. I have the following code to read an IP Forward table. It appears
my first call to "GetIPForwardTa ble" appears to work, it returns the
required buffer size in the ByteCount variable. However when I try the
second call, the one that should actually read the table the application
simply exits. This suggests a stack corruption or similar. Can anyone see
what is wrong with the code?
Dim lpDataBuffer As IntPtr
>
Dim BufferSize As Int32
>
Dim ByteCount As Int32 = Marshal.SizeOf( BufferSize)
>
Dim Result As Int32
>
'
>
' create unmanged data buffer that is too small for real data,
>
' this will force the method to return the actual byte count needed
>
'
>
lpDataBuffer = Marshal.AllocHG lobal(2)
>
Try
>
'
>
' First do a read, the buffer size is too small, this
>
' will return the needed size in the buffer size buffer
>
'
>
Result = GetIpForwardTab le(lpDataBuffer , ByteCount, True)
>
'
>
' Free the unmanged data buffer
>
'
>
Marshal.FreeHGl obal(lpDataBuff er)
>
'
>
' Create a new buffer for the real data
>
'
>
lpDataBuffer = Marshal.AllocHG lobal(5000)
>
'
>
' Read the table
>
'
>
Result = GetIpForwardTab le(lpDataBuffer , ByteCount, True)
>
Catch ex As Exception
>
MsgBox("OOPS!")
>
End Try
>
>
>
Thanks for any pointers,
>
Sid.
>
>

Sid,

It would really be nice to have a complete working example... That means
it helps to see your declare statements :)

--
Tom Shelton

[Armin Zingler]

Re: Calling unmanaged DLL issue

"Sid Price" <sid@nowhere.co mschrieb

Hello,
I am trying to call an unmanaged API (IP helper) and having problems
getting started. I have the following code to read an IP Forward
table. It appears my first call to "GetIPForwardTa ble" appears to
work, it returns the required buffer size in the ByteCount variable.
However when I try the second call, the one that should actually
read the table the application simply exits. This suggests a stack
corruption or similar. Can anyone see what is wrong with the code?

Most important: What's your declaration of GetIPForwardTab le? The rest
looks ok at first sight.



Armin