VB.Net to C++ code Marshalling

[GreenVicted]

I have a structure in VB.NET that has a dynamic array of double as a parameter.I am passing an array of structure (GElement) to a C++ DLL. I tried converting my array of GElement into a block of unmanaged memory, it works in VB.NET but crashes in my C++ DLL. I get the same error just trying to simply pass an array of GElement to my DLL instead of a Intptr, here is the error code:

0xC0000005: Access violation reading location 0x00000004

here is my function and structure in the DLL:

void _stdcall TestGElement(GElement* ge,long& nbge)
{
	
	nbge=5;
}

struct GElement
{
   double Step2D;
  double Step3D ;
  long NBVals;
  double* donnees;
        
};

My code in VB.NET (DLL call and the structure):

 Private Declare Sub TestGElement Lib "Test_GElement_Dll" (ByVal ge As System.IntPtr, ByRef nbge As Long)

 <StructLayout(LayoutKind.Sequential)>
        Public Structure GElement
            <MarshalAs(UnmanagedType.R8)> Public Step2D As Double
            <MarshalAs(UnmanagedType.R8)> Public Step3D As Double
            <MarshalAs(UnmanagedType.U8)> Public NBVals As Long
            <MarshalAs(UnmanagedType.ByValArray)> Public Donnees() As Double
        End Structure

I know it is easier if the array inside the structure as an already defined constant size but that can't be the case here...

Can someone Help me do this plz?

 

[JohnH]

Since ByValArray requires SizeConst you could try SafeArray. Default Marshaling for Arrays

 

[GreenVicted]

I tried, still the same Error code in the DLL,i'll try with a void pointer (void*) in the C++ DLL.