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copied!<p>The struct can be declared like this:</p> <pre><code>[StructLayout(LayoutKind.Sequential)] public struct Vertex { public float x; public float y; public float z; public int ID; } </code></pre> <p>Next you need to settle on a calling convention. Your C++ code is almost certainly compiled with <code>cdecl</code>. Let's stick with that.</p> <p>The function first is easy to call from C#:</p> <pre><code>[DllImport("library.dll", CallingConvention = CallingConvention.Cdecl)] public static extern float first(Vertex[] vertices); </code></pre> <p>Note that you should not use <code>SetLastError</code> here–that's for Windows API functions. And there's no need to set the <code>CharSet</code> since there is no text here.</p> <hr> <p>Now, for <code>another</code> things get more complex. If you can allocate the memory in the C# code then that is definitely the way to go.</p> <pre><code>void PopulateVertices(Vertex *vertices, int count) { for (int i=0; i<count; i++) { vertices[i].x = .... } } </code></pre> <p>On the C# side you declare it like this:</p> <pre><code>[DllImport("library.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void PopulateVertices(Vertex[] vertices, int count); </code></pre> <p>and call it like this</p> <pre><code>Vertex[] vertices = new Vertex[2]; PopulateVertices(vertices, vertices.Length); </code></pre> <hr> <p>If you don't want to allocate on the C# side of the fence then do it like this:</p> <ol> <li>Return a pointer from the C++ code and allocate it with <code>CoTaskMemAlloc</code>.</li> <li>In C# declare the return value of the imported function as <code>IntPtr</code>.</li> <li>Use <code>Marshal.PtrToStructure</code> and some pointer arithmetic to marshal the return array into a C# array.</li> <li>Call <code>Marshal.FreeCoTaskMem</code> to free the memory allocated in the native module.</li> </ol> <p>But if you want my advice, try and stick to allocating the array in the managed code.</p>

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