Delphi DLL in C# - var array as parameter

Question

i need use a Delphi DLL in my C# code.

I have some success when using other methods with common parameters, but in this case the solution still hidden.

The DLL documentation presents this declaration:

Function Get_Matrix (var Matrix : array [ 1..200 ] of char) : boolean ; stdcall;

I tried to use:

[DllImport("DLL.dll")]
public static extern bool Get_Matrix(ref char[] Matrix);

Not successful. Some Help?

David Heffernan · Accepted Answer · 2011-02-24 17:19:46Z

8

The first thing you need to do is to use stdcall on the C# side:

[DllImport("DLL.dll", CallingConvention=CallingConvention.StdCall,
    CharSet=CharSet.Auto)]

I'd also want to be sure that the Delphi side is post Delphi 2009 and so uses wide characters. If so, then there's no issue there. If you are using a non-Unicode Delphi then you'd need CharSet.Ansi.

I'd probably also return a LongBool on the Delphi side and marshal it with

[return: MarshalAs(UnmanagedType.Bool)]

back on the .NET side.

Finally, the fixed length array needs to be marshalled differently. The standard approach for fixed length character arrays is to use a StringBuilder on the .NET side which is marshalled as you desire.

Putting it altogether, and fixing your Delphi syntax, gives:

Delphi

type
  TFixedLengthArray = array [1..200] of char;

function Get_Matrix(var Matrix: TFixedLengthArray): LongBool; stdcall;

C#

[DllImport("DLL.dll", CallingConvention=CallingConvention.StdCall,
    CharSet=CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool Get_Matrix(StringBuilder Matrix);

static void Main(string[] args)
{
    StringBuilder Matrix = new StringBuilder(200);
    Get_Matrix(Matrix);
}

Finally, make sure that you null-terminate your string when you return it from your DLL!

edited Feb 24, 2011 at 17:19

answered Feb 24, 2011 at 13:52

David Heffernan

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2 Comments

Andre Soares Over a year ago

Hi, the problem stills. This seems to be relative to the "char array", when i declare the import with no parametersthe program still running, but when i declare the char parameter

David Heffernan Over a year ago

Hi, I wasn't thinking straight before. I'd forgotten about the array marshalling. I believe that the updated answer will do the job for you.

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