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 "GetIPForwardTable" 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.AllocHGlobal(2)

Try

'

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

' will return the needed size in the buffer size buffer

'

Result = GetIpForwardTable(lpDataBuffer, ByteCount, True)

'

' Free the unmanged data buffer

'

Marshal.FreeHGlobal(lpDataBuffer)

'

' Create a new buffer for the real data

'

lpDataBuffer = Marshal.AllocHGlobal(5000)

'

' Read the table

'

Result = GetIpForwardTable(lpDataBuffer, ByteCount, True)

Catch ex As Exception

MsgBox("OOPS!")

End Try

Thanks for any pointers,

Sid.

[Tom Shelton]

On 2008-05-02, Sid Price <si*@nowhere.comwrote:

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 "GetIPForwardTable" 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.AllocHGlobal(2)

Try

'

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

' will return the needed size in the buffer size buffer

'

Result = GetIpForwardTable(lpDataBuffer, ByteCount, True)

'

' Free the unmanged data buffer

'

Marshal.FreeHGlobal(lpDataBuffer)

'

' Create a new buffer for the real data

'

lpDataBuffer = Marshal.AllocHGlobal(5000)

'

' Read the table

'

Result = GetIpForwardTable(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]

"Sid Price" <si*@nowhere.comschrieb

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 "GetIPForwardTable" 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 GetIPForwardTable? The rest
looks ok at first sight.

Armin