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POC# calling Delphi DLL that returns structure within structure
 

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    <p>Yet another Delphi interop question......</p> <p>I have this Delphi code:</p> <pre><code>library DelphiDll; uses Dialogs, SysUtils, Classes; type TestEnum = (teOne, teTwo); TTestRecord = record end; TTestType = record MyTestRecords: array [1..255] of TTestRecord; MyTestEnum: TestEnum; end; {$R *.res} function DllFunction(var testType: TTestType): Boolean stdcall; export; begin testType.MyTestEnum := teTwo; Result := True; end; exports DllFunction; begin end. </code></pre> <p>And this C# code:</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.InteropServices; namespace DelpiDllTester { public enum TestEnum { One, Two } [StructLayout(LayoutKind.Sequential)] public struct TestType { [MarshalAs(UnmanagedType.ByValArray, SizeConst = 255)] public TestRecord[] MyTestRecords; public TestEnum MyTestEnum; } [StructLayout(LayoutKind.Sequential)] public struct TestRecord { } class Program { [DllImport("DelphiDll.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi)] public static extern bool DllFunction(ref TestType testType); static void Main(string[] args) { TestType testType = new TestType(); bool dllFunctionResult = DllFunction(ref testType); Console.WriteLine(dllFunctionResult); Console.WriteLine(testType.MyTestEnum); Console.ReadLine(); } } } </code></pre> <p>When I run the C# code, the console output for testType.MyTestEnum is always the enum value One even though it is clearly set to Two in the Delphi code.</p> <p>Now, if I simply change from using the array of TestRecord structures in the TestType structure to using a simple array of integers, all is well.</p> <p>Why does the array of integers work yet the array of structures does not?</p>
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