Using functions in a VC++ 6.0 MFC DLL

[alexgm23]

I have a VC++ 6.0 MFC DLL I developed long time ago and I need to use it on a C# project. I can't re-develop it again in C# because it's too BIG (160 different classes and 540 functions) and I can't spend time on that.

I know how to instatiate the C++ classes that are in that DLL, here is a sample code:

//Sample.h
 
public class __declspec(dllexport) Sample
{
public: 
    Sample(int Value);
    virtual ~Sample();
    int GetValue();
    CString & AsString();
 
private: 
    int m_iValue;
    CString m_sValue;
};
 
//---------------------------------------------------------------
 
//Sample.cpp
 
Sample::Sample(int Value)
{
    m_iValue = Value;
    m_sValue.Format("AsString: %i", m_iValue);
}
 
Sample::~Sample()
{
}
 
int Sample::GetValue()
{
    return m_iValue;
}
 
CString & Sample::AsString()
{
    return m_sValue;
}
 
//-----------------------------------------------------------------
 
//Form1.cs
 
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        LoadSample();
    }
 
    public void LoadOldMFC()
    {
        Sample s = new Sample(450);
        textBox1.AppendText(s.GetValue().ToString() + "\r\n");
        textBox1.AppendText(s.AsString() + "\r\n");
    }
}
 
[StructLayout(LayoutKind.Sequential, Pack = 4)]
public unsafe struct __Sample
{
    public IntPtr* _vtable;
    public int m_Value;
}
 
public unsafe class Sample : IDisposable
{
    private __Sample* _cpp;
 
    [DllImport("OldMFC.dll", EntryPoint = "??0Sample@OldMFC@@QAE@H@Z", CallingConvention = CallingConvention.ThisCall)]
    private static extern int _Sample_Constructor(__Sample* ths, int Value);
 
    [DllImport("OldMFC.dll", EntryPoint = "??1Sample@OldMFC@@UAE@XZ", CallingConvention = CallingConvention.ThisCall)]
    private static extern void _Sample_Destructor(__Sample* ths);
 
    [DllImport("OldMFC.dll", EntryPoint = "?GetValue@Sample@OldMFC@@QAEHXZ", CallingConvention = CallingConvention.ThisCall)]
    private static extern int _Sample_GetValue(__Sample* ths);
 
    [DllImport("OldMFC.dll", EntryPoint = "?AsString@Sample@OldMFC@@QAEAAV?$CStringT@DV?$StrTraitMFC_DLL@DV?$ChTraitsCRT@D@ATL@@@@@ATL@@XZ", CallingConvention = CallingConvention.ThisCall)]
    private static extern string _Sample_AsString(__Sample* ths);
 
    public Sample(int Value)
    {
        _cpp = (__Sample*)Memory.Alloc(sizeof__Sample));
        _Sample_Constructor(_cpp, Value);
    }
 
    public void Dispose()
    {
        _Sample_Destructor(_cpp);
        Memory.Free(_cpp);
    }
 
    public int GetValue()
    {
        return _Sample_GetValue(_cpp);
    }
 
    public string AsString()
    {
        return _Sample_AsString(_cpp);
    }
}
 

I have no problem on instantiating the class or calling function GetValue, but when I call function AsString, I only get garbage.

Someone knows how can I have this working?
Is there something I'm missing?
Is there some way to "cast" MFC class CString to System.String?

Alex G.