I whish to use a DLL I have created in VC++ so I have put the DLL in my system32 directory and declared the function I whish to use as follows:

Private Declare Function testFunc Lib _
"CalibrationDLL" (num As Integer) As Integer

the prototype in the DLL is:

extern "C" {
    int DLLDIR testFunc(int Num);
}

I then call the function in the code like this:

testResult = testFunc(1)

However, this throws and a run time error of:

Bad DLL calling convention.

What have I missed?

Cheers

The problem is name decoration, that is you have to tell the compiler that the names of the methods should be left "as is", something like:

__declspec(dllexport) int testFunc(int Num)
{
}

and because you want to pass parameters to the methods, do not forget to generate the .def file.
Marco

That's what the DLLDIR macro does. the problem was that I needed to add__stdcall in front of the the function within the DLL.