将结构数组从c＃传递给delphi

Question

I am using Robert Giesecke Unmanaged Exports 1.2.6 in VS2010 and my goal is to pass an array of structs from c# (.NET 3.5) to delphi (D7) . I have to admit, that I'm not that familiar with delphi.

I've already read this post , but the suggested answer didn't work for me: When calling func in delphi the CPU-debugging-window opens and if I continue the app exits without exception and without the desired result.

Here is the code I tried:

C# platform x86

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using RGiesecke.DllExport;

namespace ArrayTest
{
    public class Class1
    {
        public struct Sample
        {
            [MarshalAs(UnmanagedType.BStr)]
            public string Name;
        }

        [DllExport]
        public static int func(
            [Out, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)]
            Sample[] samples,
            ref int len
        )
        {
            // len holds the length of the array on input
            // len is assigned the number of items that have been assigned values 
            // use the return value to indicate success or failure
            for (int i = 0; i < len; i++)
                samples[i].Name = "foo: " + i.ToString();
            return 0;
        }
    }
}

Delphi7

program DelphiApp;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  ActiveX;

type
  TSample = record
    Name: WideString;
  end;
  PSample = ^TSample;

function func(samples: PSample; var len: Integer): Integer; stdcall;
  external 'ArrayTest.dll';

procedure Test2;
var
  samples: array of TSample;
  i, len: Integer;
begin
  len := 10;
  SetLength(samples, len);
  if func(PSample(samples), len)=0 then
    for i := 0 to len-1 do
      Writeln(samples[i].Name);
end;

begin
  Test2();
end.

As mentioned earlier, the debugger opens the CPU-Window and if I continue the app exits without exception or error message. If I run it without dbugger, Windows tells me the app isn't working any more and the app closes.

What am I missing?

Update

Modified code:

[DllExport]
public static int func(
    [Out, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)]
    Sample[] samples,
    ref int len
)
{
    Console.WriteLine("return 0");
    return 0;
}

procedure Test2;
var
  samples: array of TSample;
  i, len: Integer;
begin
  len := 10;
  SetLength(samples, len);
  if func(PSample(samples), len)=0 then
    for i := 0 to len-1 do
      Writeln('D7: ', i);
end;

Even if I don't access the array on either side, the behaviour still is the same.

Console-output: return 0

Answer 1

Seems like I found the issue:

The code runs fine if .NET 4.0 or higher is used. If you use .NET 3.5 or lower the len-parameter has to be passed by value.

See MSDN-documentation SizeParamIndex v3.5 :

The parameter containing the size must be an integer that is passed by value.

See MSDN-documentation SizeParamIndex v4.0 :

When arrays are passed as C-style arrays, the marshaler cannot determine the size of the array. Therefore, to pass an managed array to an unmanaged function or method, you must provide two arguments:

• The array, defined by reference or value.

• The array size, defined by reference or value.

Code working with .NET 3.5:

C#

[DllExport]
public static int func(
    [Out, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)]
    Sample[] samples,
    int len,
    ref int outLen
)
{
    // len holds the length of the array on input
    // outLen is assigned the number of items that have been assigned values 
    // use the return value to indicates success and the required array size (>=0) or failure (<0)
    int requiredSize = 20;
    if (requiredSize < len)
    {
        len = requiredSize;
    }
    for (outLen = 0; outLen < len; outLen++)
    {
        samples[outLen].Name = "foo: " + outLen.ToString();
    }
    return requiredSize;
}

Delphi7

function func(samples: PSample; len: Integer; var outLen: Integer): Integer; stdcall;
  external 'ArrayTest.dll';

procedure Test2;
var
  samples: array of TSample;
  i, len: Integer;
begin
  len := 0;
  // query the required array size
  i := func(PSample(samples), len, len);
  if i>0 then
  begin
    len := i;
    SetLength(samples, len);
    if func(PSample(samples), len, len)>=0 then
      for i := 0 to len-1 do
        Writeln(samples[i].Name);
  end;
end;

Conclusion:

The code posted in my question and posted by David Heffernan here only works with .NET >= 4.0! If you have to use .NET <= 3.5 you must pass the arraysize by value and not by reference!