C#

// Start with Car.Engine equal to addr0
// Set variable newEngine to addr1
Engine newEngine = new Engine(200, "PS");
// Set variable oldEngine to 0 (null)
Engine oldEngine = null;
// Set variable oldEngine to addr0
oldEngine = Car.Engine;
// Set variable Car.Engine to addr1
Car.Engine = newEngine;
...
// Set variable Car.Engine to addr0
Car.Engine = oldEngine;
// At this point, the following is true:
// Car.Engine = addr0
// oldEngine  = addr0
// newEngine  = addr1

Luc Pattyn wrote:

if all it does is GC.Collect() then you are right of course

Luc Pattyn wrote:

As for unmanaged resources, it is still not clear to me; my advice is to call Dispose() or Close()

protected override void WndProc(Message m)
{
    //m contains the message 'm.Msg'
    //the Lparam and Wparam m.(L/W)param
    //and a method for getting the object in
    //th Lparam, it also contains the result.

    //You need to have this line, unless you are canceling a message
    base.WndProc(ref m);
}

object value = cmd15.ExecuteScalar();
if (value != DBNull.Value)
{
  max = Convert.ToInt32(value);
}
max++;

f4hd wrote:

dll while
the same code works fine in a normal console application!

f4hd wrote:

The exception that I get is System.NullReferenceException. Which is access violation I assume

f4hd wrote:

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, float[,] output, int nFrames,int featureWidth);

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, [In,Out] ref float[,] output, int nFrames, int featureWidth);

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, [Out] out float[,] output, int nFrames, int featureWidth);

f4hd wrote:

not quite elegant, is to convert the 2d arrays into 1d arrays during passing and receiving... Can there be any better way I wonder?

DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(IntPtr [] input, IntPtr[] output, int nFrames,int featureWidth);
private float[,] foo()
{
    int nFrames = 3; // change these 2 values to appropriate vals
    int featurWidth = 5; // ...
    float[,] myArray = new float[2,nFrames];
    // fill your values here...
    IntPtr[] input = writeArray(myArray);
    IntPtr[] output = allocArray(featurWidth);
    bool ok = Evaluate(input, output, nFrames, featurWidth);
    freeArray(input);
    return readArray(output,featurWidth);
}
private float[,] readArray(IntPtr[] Items, int featureWidth)
{
    float[,] RetVal = new float[2,featureWidth];
    readMemArray(Items[0],RetVal,0,featureWidth);
    readMemArray(Items[1],RetVal,1,featureWidth)
    freeArray(Items);
    return RetVal;
}
private void readMemArray(IntPtr Pointer, Float[,] Target, int Dimension, int featureWidth)
{
   float[] Dummy = new float[featureWidth];
   Marshal.Copy(Pointer,Dummy,0,featureWidth);
   copyArray(Dummy, Target, Dimension);
}
private void freeArray(IntPtr[] Items)
{
    Marshal.FreeHGlobal(Items[0]);
    Marshal.FreeHGlobal(Items[1]);
}
private IntPtr[] allocArray(int ItemCount)
{
    IntPtr RetVal = new IntPtr[2];
    int Count = Marshal.SizeOf(typeof(float)) * ItemCount;
    RetVal[0] = Marshal.AllocHGlobal(Count);
    RetVal[1] = Marshal.AllocHGlobal(Count);
    return RetVal;
}
private IntPtr[] writeArray(float[,] Array)
{
    IntPtr[] RetVal = allocArray(Array.GetLength(1));
    float[] Dummy = new float[Array.GetLength(1)];
    copyArray(Array, Dummy, 0);
    Marshal.Copy(Dummy,0,RetVal[0],Dummy.Length);
    copyArray(Array, Dummy, 1);
    Marshal.Copy(Dummy,0,RetVal[1],Dummy.Length);
}
private void copyArray(float[] Source, float[,] Destination, int zDimIndex)
{
    for(int i = 0; i< Source.Length; i++)
    {
        Destination[zDimIndex,i] = Source[i];
    }
}
private void copyArray(float[,] Source, float[] Destination, int zDimIndex)
{
    for(int i = 0; i < Destination.Length; i++)
    {
        Destination[i] = Source[zDimIndex,i];
    }
}