I have a DLL (not .NET) that takes a function pointer argument and calls
that function with an integer argument. The DLL is being called from C#.



So far, it is partially working, but the integer argument is getting
corrupted (MessageBoxes in the dll and C# fire).

I do not understand why the int parameter is getting corrupted calling the
callback function (Testing() in C#). ( probably I just don't understand
what I'm doing :-) )



If anyone could give me some help I'd be eternally greatful...



David



Here's the setup:



The DLL:

extern "C"

{

__declspec(dllexport) int __stdcall ExecuteCallback(int (*
pFunction)(int), int val)

{

MessageBox(NULL, "Got here", "got here", MB_OK);
// this fires ok



// val == 10 here - no corruption until inside the
callback

return (*pFunction)(val);

}

}



In C#:

namespace CsDriver

{

public class TestDlls

{

public TestDlls()

{

}



[DllImport("CallbackDll.dll",
CallingConvention=CallingConvention.StdCall)]

public static extern Int32 ExecuteCallback(IntPtr
pFunction, Int32 val2);

}

}



C# calling function:

private void OnTestItClick(object sender,
System.EventArgs e)

{

// delegate declaration:

// public delegate int
CallbackDelegate(int val);

CallbackDelegate cd = new
CallbackDelegate(Testing);



// get the function pointer

IntPtr fPtr =
cd.Method.MethodHandle.GetFunctionPointer();



int val = TestDlls.ExecuteCallback(fPtr,
10); // return value corrupted

MessageBox.Show(val.ToString());

}



private static int Testing(int val)

{

// parameter val is corrupted here!!!!

// val == 2012581943, not 10 as it
should



MessageBox.Show("In Testing()"); //
MessageBox fires ok

return val;

}

David,

> __declspec(dllexport) int __stdcall ExecuteCallback(int (*
>pFunction)(int), int val)

If you can modify the C source, you should change

int (*pFunction)(int)

to

int (__stdcall *pFunction)(int)


> [DllImport("CallbackDll.dll", CallingConvention=CallingConvention.StdCall)]
> public static extern Int32 ExecuteCallback(IntPtr pFunction, Int32 val2);

Change the first parameter type to CallbackDelegate. The runtime takes
care of marshaling it to a function pointer.



Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/
Please reply only to the newsgroup.

Hi, David:
I suggest you declare delegate instead of IntPtr for the
function pointer in your dllimport. I think it will handle some marshal
issues which easily cause problems if you handle them by yourself.


[DllImport("CallbackDll.dll", CallingConvention=CallingConvention.StdCall)]
public static extern Int32 ExecuteCallback(CallbackDelegate callback, Int32
val2);


Hope it helps!
Qiu




"David Rose" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I have a DLL (not .NET) that takes a function pointer argument and calls
> that function with an integer argument. The DLL is being called from C#.
>
>
>
> So far, it is partially working, but the integer argument is getting
> corrupted (MessageBoxes in the dll and C# fire).
>
> I do not understand why the int parameter is getting corrupted calling the
> callback function (Testing() in C#). ( probably I just don't understand
> what I'm doing :-) )
>
>
>
> If anyone could give me some help I'd be eternally greatful...
>
>
>
> David
>
>
>
> Here's the setup:
>
>
>
> The DLL:
>
> extern "C"
>
> {
>
> __declspec(dllexport) int __stdcall ExecuteCallback(int (*
> pFunction)(int), int val)
>
> {
>
> MessageBox(NULL, "Got here", "got here", MB_OK);
> // this fires ok
>
>
>
> // val == 10 here - no corruption until inside the
> callback
>
> return (*pFunction)(val);
>
> }
>
> }
>
>
>
> In C#:
>
> namespace CsDriver
>
> {
>
> public class TestDlls
>
> {
>
> public TestDlls()
>
> {
>
> }
>
>
>
> [DllImport("CallbackDll.dll",
> CallingConvention=CallingConvention.StdCall)]
>
> public static extern Int32 ExecuteCallback(IntPtr
> pFunction, Int32 val2);
>
> }
>
> }
>
>
>
> C# calling function:
>
> private void OnTestItClick(object sender,
> System.EventArgs e)
>
> {
>
> // delegate declaration:
>
> // public delegate int
> CallbackDelegate(int val);
>
> CallbackDelegate cd = new
> CallbackDelegate(Testing);
>
>
>
> // get the function pointer
>
> IntPtr fPtr =
> cd.Method.MethodHandle.GetFunctionPointer();
>
>
>
> int val =
TestDlls.ExecuteCallback(fPtr,
> 10); // return value corrupted
>
> MessageBox.Show(val.ToString());
>
> }
>
>
>
> private static int Testing(int val)
>
> {
>
> // parameter val is corrupted here!!!!
>
> // val == 2012581943, not 10 as it
> should
>
>
>
> MessageBox.Show("In Testing()"); //
> MessageBox fires ok
>
> return val;
>
> }
>
>
>
>