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POMarshalling from C# to a DLL with a TCHAR** x[] parameter
 

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  1. POMarshalling from C# to a DLL with a TCHAR** x[] parameter
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    <p>I am trying to call a Win32 DLL from some C#. The DLL function is declared as follows:</p> <pre class="lang-c prettyprint-override"><code>extern "C" __declspec(dllexport) UINT foo(TCHAR** list[], int&amp; listSize, TCHAR* error); </code></pre> <p>In C#, I declare the external function like so:</p> <pre class="lang-cs prettyprint-override"><code>[DllImport("foo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)] static extern uint foo(StringBuilder[] list, ref int listSize, StringBuilder error); </code></pre> <p>My problem has to do with the <em>list</em> parameter, which is an array of StringBuilder classes.</p> <p>Some test code where I call the DLL function is as follows: (Note: I realise that there are boundary checks missing, etc. At this stage, I am just trying to get things working).</p> <pre class="lang-cs prettyprint-override"><code>// allocate a buffer for a possible error message being returned StringBuilder error = new StringBuilder(1000); // allocate buffers for the list of strings returned StringBuilder[] list = new StringBuilder[10]; for (int i = 0; i &lt; 10; i++) { list[i] = new StringBuilder(1000); } int listSize = list.Length; uint result = foo(list, ref listSize, error); </code></pre> <p>Passing the StringBuilder as a buffer for the <em>error</em> parameter, works fine. I can set its contents in the DLL as follows:</p> <pre class="lang-cpp prettyprint-override"><code>_tcscpy(error, _T("Something went wrong"); </code></pre> <p>When the C# call to <em>foo</em> returns, the <em>string error</em> variable has the text we set it to in the DLL.</p> <p>But, I cannot work out how to marshal the <em>StringBuilder[] list</em> parameter.</p> <p>In the C++, I am able to set the contents of the <em>list</em> array:</p> <pre class="lang-cpp prettyprint-override"><code>_tcscpy((*list)[0], _T("First item")); // and so on... </code></pre> <p>And, even though there is no crash that occurrs due to any possible problematic marshalling, the <em>list</em> in the C#, when the call to <em>foo()</em> returns, does not contain any of the strings we set in the C++.</p> <p>I'm guessing that the problem is with the <em>DllImport</em> and how I've declared the <em>list</em> parameter should be marshalled.</p> <p>By the way, the example DLL has a matching function which one would then call to deallocate the "TCHAR** list" returned by the example <em>foo</em> shown above. </p>
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    1. USDiego Barros
    1. USDiego Barros
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    1. CO`TCHAR** list[]`? Do you have an array of strings, or an array of an array of strings?
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      1. USMohammad Dehghan
    2. COAn array of pointers which point to pointers to TCHARs. Confusing, I know.
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      1. USDiego Barros
    3. COSo why did you define the managed signature as `StringBuilder[]`? This is equivalent of `TCHAR **` I guess. But neither will work in your case :).
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      1. USMohammad Dehghan
 

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