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POC++ managed code calling unmanaged code with handles
 

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  1. POC++ managed code calling unmanaged code with handles
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    <p>After an afternoon of searching this problem has got me stumped! I'm writing a managed C++ application which needs to call some unmanaged code. This is the function I need to call:</p> <pre><code>public: void Connect( [out] LONG* pCookieID, [out] LONG* pNumberOfStreams, [out] VARIANT* pMediaType ); </code></pre> <p>And the documentation has this note: Parameter <code>pMediaType</code> must be set to null in <code>C#</code> and nothing in <code>VB .NET</code> before calling Connect, otherwise an exception with error code <code>DISP_E_TYPEMISMATCH = 0x80020005</code> will be thrown.</p> <p>So I need to pass 3 handles to the function for it to return data in them. The two <code>LONG</code> handles seem reasonably straightforward but I can't figure out how to pass a handle for a variant. </p> <p>This is where I've got to:</p> <pre><code>int ^cookieID; int ^numberOfStreams; System::Object ^buffer; GCHandle hcookieID = GCHandle::Alloc(cookieID, GCHandleType::Pinned); GCHandle hnumberOfStreams = GCHandle::Alloc(numberOfStreams, GCHandleType::Pinned); GCHandle hbuffer = GCHandle::Alloc(buffer, GCHandleType::Pinned); parser-&gt;Connect(hcookieID.AddrOfPinnedObject().ToInt32(), hnumberOfStreams.AddrOfPinnedObject().ToInt32(), (System::Object^)hbuffer.AddrOfPinnedObject().ToInt32()); hcookieID.Free(); hnumberOfStreams.Free(); hbuffer.Free(); </code></pre> <p>The compiler accepts this but when the <code>Connect</code> method is called I get the following error: </p> <blockquote> <p><code>"Type mismatch. (Exception from HRESULT: 0x80020005</code> <br> <code>(DISP_E_TYPEMISMATCH))"} System::Exception^</code></p> </blockquote> <p>I've searched high and low and tried all sorts of solutions but I can't find any. </p>
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    1. USAdam
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    1. COWouldn't it be easier to call the unmanaged function directly from C++, rather than going through the P/Invoke layer?
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      1. USTim Robinson
    2. CODon't use the hat for value types!!! These are not handles, the argments are simply passed by reference. The *ref* keyword in C#, & in C++/CLI.
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      1. USHans Passant
    3. COThanks but I'm not sure I understand these 2 comments. The ^ seem to be necessary to allow the variables to be changed into fixed pointer locations using GCHandle and I have no preference on how I call the method but seeing as my calling code is managed but the called funciton is unmanaged I've got to jump through whatever hoops are necessary to allow the arguments to be passed as references so that the called method can load them with the values it returns. I'm just looking for the simplest way to acheive this. C++ seems to make this far more painful than if I was using C#!
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      1. USAdam
 

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