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copied!<p><code>GCHandle.Alloc</code> <a href="http://msdn.microsoft.com/en-us/library/a95009h1.aspx" rel="nofollow noreferrer"><em>"Allocates a Normal handle for the specified object"</em></a>, which <em>"creates a handle to a managed object ... which prevents the managed object from being collected"</em>.</p> <p>What you're looking for is the methods from <code>System.Runtime.InteropServices.Marshal</code>, which allow you to do things like copy managed objects to memory accessible by unmanaged code. Unfortunately, according to <a href="http://msdn.microsoft.com/en-us/library/0szztey7%28VS.80%29.aspx" rel="nofollow noreferrer">this</a>, the pointers in your struct make it a little harder to marshal than many other things (in the sense that many other things can be automatically marshalled using the appropriate P/Invoke attributes), but it's still possible. I've tried this out and it works:</p> <pre><code>APP_PARAM param = new APP_PARAM(); string[] text = new string[] { "A", "B", "C" }; param.numData = text.Length; // Manually allocate an array of pointers, one for each string. arr holds the array's address. IntPtr arr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)) * text.Length); try { param.text = arr; IntPtr[] unmanagedText = new IntPtr[text.Length]; try { // Create a null-terminated ANSI string in unmanaged memory for each element in text. for (int i = 0; i < text.Length; i++) unmanagedText[i] = Marshal.StringToHGlobalAnsi(text[i]); // Copy the addresses of the unmanaged strings into the manually allocated array. // I don't know of any way to make an unmanaged copy of a managed array in one call. Marshal.Copy(unmanagedText, 0, arr, unmanagedText.Length); // param now looks like what the C++ code is expecting (except for the array of int). StartApp(param); } finally { foreach (IntPtr str in unmanagedText) Marshal.FreeHGlobal(str); } } finally { Marshal.FreeHGlobal(arr); } </code></pre> <p>You'll have to have similar allocation/free code for your array of int values, with its own try/finally blocks to make sure FreeHGlobal is called.</p>

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