Jason Newell wrote:
> All,
>
> I'm authoring a C++ .dll & C# .dll and need a little help. I am
> experienced in interop but this one has me stumped. Does anyone have a
> simple example of how to declare a C++ exported function that can return
> a struct array in one of the parameters to C#? The C# .dll would have
> no idea how many elements would be returned so the C++ .dll would need
> to dynamically allocate the array and populate it. I fully expect to be
> told that I'm doing things wrong but I'm just looking for advice on how
> to do this correctly.
>
> Here's what I have now.
>
> [C++ .h]
> struct MyStruct {
> DWORD dwA;
> double dA;
> double dB;
> DWORD dwB;
> DWORD dwC;
> };
>
> extern "C" __declspec(dllexport) HRESULT GetStructArray(MyStruct* structs);
>
> [C++ .cpp]
> extern "C" __declspec(dllexport) HRESULT GetStructArray(MyStruct* structs)
> {
> structs = (MyStruct)CoTaskMemAlloc(sizeof(MyStruct) * 4);
> /* structs gets populated */
> }
>
> [C# .cs]
> [StructLayout(LayoutKind.Sequential)]
> public struct MyStruct
> {
> public uint dwA;
> public double dA;
> public double dB;
> public uint dwB;
> public uint dwC;
> };
>
> [DllImport(@"CPlus.dll"]
> private static extern int GetStructArray(out MyStruct structs);
>
> public void Test()
> {
> MyStruct[] structs;
> GetStructArray(out structs);
> }
>
>
> I'm even open to returning an array of pointers and using
> Marshal.PtrToStructure() if need be.
>
> Thanks so much!
>
> Jason Newell