How can i pass struct (with string) from unmanaged ?

[Zeki-Gursoy]

Hello.
I need pass UDT from VBA to c# dllexport function. But not show anything.

C# side:
[code]
using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace ClassLibrary1
{
public unsafe class Class1
{
[DllExport(CallingConvention.StdCall)]
public static void test(ref Record rec)
{

        MessageBox.Show(rec.Value + "");
    }


}

[ComVisible(true)]
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public unsafe struct Record
{
    [MarshalAs(UnmanagedType.LPStr)]
    public string Value;
}

}
[/code]

Excel VBA side (bas module):

`Type Record2
Name As String
Value As String
End Type

Private Declare PtrSafe Sub test Lib "C:\mypath\ClassLibrary1.dll" (ByRef rec2 As Record2)

Sub deneme()
Dim r As Record2

r.Value = "zeki"

test r

End Sub`

[3F]

Hello Zeki,

It's hard to tell how marshalling is going without debugging in your case when you're trying to refer it as an actual clr type.
For this case or such I recommend to use IntPtr because it exactly allows you to fully control the process step by step.

In your VBA script you can change the Declare signature to LongPtr same like I suggested here #189 (comment)
Note also you don't need unsafe context.

For IntPtr control your structure either through PtrToStructure() or use Conari like:

[DllExport(CallingConvention.StdCall)]
public static void test(IntPtr ptr)
{
    ptr.Native().f<CharPtr>("s")._.s // (CharPtr)"zeki"
}

If strong typing is required,

public struct Record { public string Value; }
//...
using NativeStruct<Record> nst = new(ptr); // nst.Data.Value == "zeki"

or almost the same but generated at runtime (i.e. without declaring the actual at compile time)

ptr.Native().f<CharPtr>("Value").build(out dynamic record);
//dynamic record = ptr.Native().f<CharPtr>("Value").Struct.Access;

Here you can find updated tests for strings, arrays, and structures:
https://github.com/3F/DllExport/blob/master/src/DllExport/assets/NetfxAsset/Basic.cs

[Zeki-Gursoy]

Thank you for reply.

Regards,