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Message |
chris123
Joined: 27 Aug 2011
Posts: 3
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 Posted: Sat Aug 27, 2011 4:51 pm Post subject: Guidance needed with PInvoke with pointers |
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Hi,
I am trying to interface a native DLL with my VB.Net application using PInvoke. I think I have several of the simpler methods working ok, but am struggling with an initialization method that uses pointers.
The method is described as:
| Code: |
INT32 InitialCommon ( UINT8 *name, INT32 *func )
UINT8 *name Own name (maximum 8 characters)
INT32 *func; Pointer storing function code to be used
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and the DLL comes with some sample code:
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INT32 func[3];
int ret;
UINT8 name[8+1] = {"ComputerName"};
ret = InitialCommon( name, func );
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I think I need
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<DllImport("C:\ChartPlot\bin\dll\Fnet.dll", EntryPoint:="_InitialCommon@8", _
SetLastError:=True, CharSet:=CharSet.Unicode, _
ExactSpelling:=True, _
CallingConvention:=CallingConvention.StdCall)> _
Public Shared Function InitialCommon(ByVal pntName As IntPtr, ByVal pntFunc As IntPtr) As Int32
End Function
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I have tried:
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Dim pntName As IntPtr = Marshal.StringToHGlobalAnsi("ComputerName")
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to create the first pointer, with various ways of creating the second pointer, including:
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Dim func(2) As Integer
Dim gcHandle As GCHandle = gcHandle.Alloc(func, GCHandleType.Pinned)
Dim pntFunc As IntPtr = gcHandle.AddrOfPinnedObject()
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However with all the options I have tried I keep getting
| Quote: |
Attempted to read or write protected memory. This is often an indication that other memory is corrupt. |
Which I believe is due to a mismatch somewhere.
Can anyone point me in the right direction please?
Thanks
Chris |
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Brian Donahue
Joined: 23 Aug 2004
Posts: 6369
Location: Red Gate Software
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| Posted: Mon Aug 29, 2011 10:34 am Post subject: |
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It looks like "name" is a fixed-size buffer of 9 bytes rather than a pointer. I'd try declaring name as a byte array rather and an intptr and use System.Text.ASCIIEncoding.GetByteArray() on your string and make sure it isn't bigger than 9 bytes.
_________________
Brian Donahue
Technical Support
Red Gate Software Ltd.
44 (0)870 160 0037 ext 8521
US and CAN 1-866-RED GATE ext 8521 |
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chris123
Joined: 27 Aug 2011
Posts: 3
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| Posted: Tue Aug 30, 2011 10:26 pm Post subject: |
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Thanks for the guidance - as you may have realised my knowledge of C is very limited, I took the asterisk to mean that the variable was a pointer.
I will try a byte array and let you know.
Thanks
Chris |
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Brian Donahue
Joined: 23 Aug 2004
Posts: 6369
Location: Red Gate Software
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| Posted: Wed Aug 31, 2011 9:28 am Post subject: |
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Yeah, in C you would probably pass in &name, which would pass in the address. I think Marshal calls do this stuff automagically.
_________________
Brian Donahue
Technical Support
Red Gate Software Ltd.
44 (0)870 160 0037 ext 8521
US and CAN 1-866-RED GATE ext 8521 |
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chris123
Joined: 27 Aug 2011
Posts: 3
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| Posted: Wed Sep 07, 2011 11:16 pm Post subject: |
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Yes, that sorted it. Many thanks for your help.
Chris |
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