从C＃.Net 2010 Pinvoke VB6函数

Question

I want to PInvoke a function written in VB6 from C#. We can call this function in VB6 like this:

Declare Function ApplyNNet Lib " location of the DLL file" (MyNNetType As String, MyAddress As String, MyInput() As Double) As Variant

My code in C# is:

[DllImport("NNetApply.dll", EntryPoint = "ApplyNNet", CallingConvention = CallingConvention.StdCall)] 
public static extern IntPtr ApplyNNet(string type, string add, double[,] data);
//run ANN with data
string address = @"C:\Users\PNGE-User\Desktop\Faegheh\Project\Neural Network For Pressure Vs q,x,y\P ve x,y,q\P ve x,y,q";
        double[,] P = new double[no_data,2];
        var P_ = ApplyNNet("Back Prop", address, data);

When I debug my code, an error appears:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

Answer 1

First of all, I am assuming that the DLL was not in fact written in VB6. The fact that you show code that uses Declare to call the function contradicts that. So I am assuming that the DLL was written in some other language (eg C++) and that you are currently calling the DLL from VB6.

The VB6 code that calls the DLL is declared like this:

Declare Function ApplyNNet Lib "DLLFileName" (MyNNetType As String,
    MyAddress As String, MyInput() As Double) As Variant

Your C# version looks like this:

[DllImport("NNetApply.dll", EntryPoint = "ApplyNNet", 
    CallingConvention = CallingConvention.StdCall)] 
public static extern IntPtr ApplyNNet(string type, string add, double[,] data);

There are two obvious differences:

1. The third parameter does not match. Instead of double[,] you need double[] .
2. The return value does not match. A VB6 variant cannot be matched up with IntPtr . You need to declare the return value to be of type object in your C# code.

So the pinvoke should be:

[DllImport("NNetApply.dll")] 
public static extern object ApplyNNet(string type, string add, double[] data);

Update

With this declaration you receive a pinvoke error:

PInvoke restriction: cannot return variants.

I'm not sure how you can get around this in pinvoke. In your situation I think I would create a VB6 project that wrapped up the DLL and exposed it as a COM interface. I'd then add a COM reference to your C# project and move on.