msdn help states that for passing structures using p/invoke;
Use either a structure passed by reference or a class passed by value when the unmanaged function demands one level of indirection. and
Use a class passed by reference when the unmanaged function demands two levels of indirection.
I am calling the following 'unmanaged' C++ function from vb.net
int EXPORTED GetValues(long lSegmentIndex, sStructA * pStructA)
I need to fetch values for szName of sStructA and var1 of sStructB.
Is that 2 levels of indirection If so, do I need to lose my struct, which worked for vb6 and use a class now Thank you. greg
typedef struct sStructC
{
enumeratedValue enumeratedType;
long var1;
double var2[3];
double var3[3][3];
double var4[5][2];
double var5[5][2];
} sStructC;
typedef struct sStructB
{
long var1;
long var2;
double var3;
double var4[3];
} sStructB
typedef struct sStructA
{
char szName[128];
long var2;
long var3;
double var4[3];
double var5;
double var6[3];
double var7;
double var8;
int var9;
int var10;
sStructB var11[20];
sStructC var12;
} sStructAt;
This worked fine in vb6, The unmanaged function was called via
Public Declare Function GetValues _
Lib "foo.dll" _
(ByVal lIndex As Long, ByRef sStructA As StructA) As Long
where values to be fetched are 'name' from StructA and var1 from StructB (a field within StructA)
Public Type StructA
name As String * 128
var2(19) As StructB
and another value required is from StructB
Public Type StructB
var1 As Long
looks like a pointer to a pointer to a char. And a pointer to a struct to a struct in c++ is two layers of indirection. Correct
MSDN help for VS2005
ms-help://MS.VSCC.v80/MS.MSDN.v80/MS.VisualStudio.v80.en/dv_fxinterop/html/9b92ac73-32b7-4e1b-862e-6d8d950cf169.htm
Use a class passed by reference when the unmanaged function demands two levels of indirection.
DeamonX
As I try the class approach I get a Design Time error for the following;
Value of Type ClassB cannot be converted to '1 dimensional array of ClassB'
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> Public Class ClassB
Public var1() As Double
Public Sub New()
ReDim var1(2)
End Sub
End Class
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> Public Class ClassA
Public var1() As ClassB
Private Sub New()
ReDim var1(19)
var1 = New ClassB() <--
End Sub