Marshaling a C++ two-dimensional fixed length char array as a structure member

[TTheot]

Hallo everyone.

I am trying to call an unmanaged C++ function, that has a structure as an input parameter.
The structure is defined in the header file like this:

struct MyStruct
{
	int	 siOrder;
	char	 aaszNames[6][25];
	int     siId[6];
	int     siTones[6];		
};

I've defined the managed structure as following:

<StructLayoutAttribute(LayoutKind.Sequential, CharSet:=CharSet.[Ansi])> _
Public Structure MyStruct
    Public siOrder As Integer

    <MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst:=150)> _
    Public aaszNames As String

    <MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst:=6, ArraySubType:=UnmanagedType.I4)> _
    Public siId() As Integer

    <MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst:=6, ArraySubType:=UnmanagedType.I4)> _
    Public siTones() As Integer
End Structure

The C++ dll writes to a log file when a function is called. From this log I can see that the structure cannot be resolved.

My issues are the following:

a) Marshal.SizeOf( MyStruct) is computed as 204, but as I can see, the size seems to be: 4 + 150 + 6*4 + 6*4 = 202 bytes. What are these two extra bytes, and where are they supposed to be padded?

b) How should I populate the aaszNames field? The C++ expects 6 rows of 25 character long strings, but my individual values are of less length (eg "John", "Robert", etc). How should I concatenate the string?

Could anyone give me a hint about these issues?

[CroCrew]

Is this a C++ or VB question? If it a C++ question you would get a faster reply to your question if it were posted in the C++ section and not the VB section.

Hope you get your answer,
CroCrew~

[TTheot]

Well, I could also try the C++ section... ;)

[CroCrew]

Lets see if we can get this moved to the C++ section.

Good Luck in getting your answer,
CroCrew~

[TTheot]

Thanx CroCrew :)

Hoping for some hints myself..

[tlhintoq]

TIP: When you are writing your question, there is a button on the tool bar that wraps the [code] tags around your copy/pasted code. It helps a bunch. Its the button with a '#' on it. More on tags. They're cool. Check'em out.

[Curtis Rutland]

Thread moved. Hope you find your answers.