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I have to pass a structure with some strings and a few

arrays to a dll written in c from my VB.NET code. Any

information on how to go about doing it. Any website

addresses where related information can be found will also

be of great help.



Thanks


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"baboo" <baboo@discussions.microsoft.com>schrieb

If you've got VB/VS.NET:



<F1>

VS.NET

.NET Framework

Programming with .NET Framework

Interoperating with unmanaged code



especially these sub topics:



Consuming unmanged DLL functions

Design Considerations For Interoperation

Interop Marshalling





If you only have the SDK: msdn.microsoft.com">msdn.microsoft.com





--

Armin



learn.to/quote">learn.to/quote

www.plig.net/nnq/nquote.html">www.plig.net/nnq/nquote.html



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Thanks for the info... i looked at that information but

there is not much that will help me solve my problem which

is:



I have to pass an array of strings inside a structure,

from .NET code to a 'C' DLL, though i am able to pass the

structure.. the c code gives me garbage values for that

array.

the .NET code is:



<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)

Dim FieldNumber As Integer

Dim Dummy As Integer

Public ControlNames() As String

End Structure



The "ControlNames" array is an array of 15 strings with

each string being 50 characters long.



and the 'C' structure which takes the values is:



struct Test { double ErrorValue;

int FieldNumber;

int Dummy;

char sFixUpCtrl[15][50];

};



while debugging i find that the values for

the "ControlNames" array in 'C' are garbage.



any idea about how to go about fixing this problem??



~.~.~.~.~.~.

Baboo

On 2003-11-10, baboo <baboo@discussions.microsoft.com>wrote:

This one is a little problematic... Normally, a fixed length array or

string in side of a structure is not a problem... For example, if it

was a single 50 character string:



<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>_

Public Structure Test

Public ErrorValue As Double

Public FieldNumber As Integer

Public Dummy As Integer



<MarshalAs(UnmanagedType.ByValTStr, SizeConst:=50)>_

Public sFixUpCtrl As String

End Structure



But your's is a fixed two dimensional array. I have never had that

come up before, and I really don't see a good way to do it with in the

bounds of what is currently defined in the framework...



As a work around (unless someone comes up with a better idea, or knows a

way to do this directly), I would suggest just passing a single string

buffer big enough to hold the entire thing, and then chunk the data on

the return. In theory that should work since arrays are just contiguos

blocks of memory - even if they are 2D. So maybe something like (you

may have to play with the numbers - I'm sort of sleepy right now :)



<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>_

Public Structure Test

Public ErrorValue As Double

Public FieldNumber As Integer

Public Dummy As Integer



<MarshalAs(UnmanagedType.ByValTStr, SizeConst:=750)>_

Public sFixUpCtrl As String

End Structure



And then, just do something like:



'Call your api call

Dim st As Test

....



' chunk the string

Dim s(14) As String



For i As Integer = 0 To 14

s(i) = st.sFixUpCtrl.SubString(i*50, 50)

Next i



Oi! I'm getting sleepy... I hope I'm not doing something stupid in the

above little loop. But anyway, it's an idea that may work. I'll see if

I can find any more info on this tomorrow...



--

Tom Shelton

MVP [Visual Basic]

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