Re: Linking error in mixed code

"Alf P. Steinbach" <>
Tue, 22 Jul 2008 13:03:37 +0200

Hi all,
I have a .NET application which needs to use some Win APIs. I set the
linker option (of VC++ .NET 2008 Express) to '\clr' to use mixed code
and added the following line of code:

#pragma unmanaged
namespace UnManagedFuncs
    using namespace System::Runtime::InteropServices;

    [DllImport("user32", EntryPoint = "SetClipboardViewer", CharSet =
    extern "C" long __cdecl SetClipboardViewer(void* hWnd);

    [DllImport("user32", EntryPoint = "SetWindowLong", CharSet =
    extern "C" long __cdecl SetWindowLongW(void* hWnd, int nIndex, long

    [DllImport("user32", EntryPoint = "CallWindowProc", CharSet =
    extern "C" long __cdecl CallWindowProcW(long* lpPrevWndFunc, void*
hWnd, unsigned int uMsg, unsigned int wParam, long lParam );


#pragma managed
namespace MyApp
                  private: System::Void frmMain_Load(System::Object^
sender, System::EventArgs^ e)
                  // Register this window to receive 'clipboard contents
changed' event




I get the following linker errors:
ScratchBook.obj : error LNK2019: unresolved external symbol
_CallWindowProcW referenced in function _UnManagedWinProc
ScratchBook.obj : error LNK2019: unresolved external symbol
_SetWindowLongW referenced in function "void __cdecl
UnManagedFuncs::HookWindow(void *)" (?

What is wrong?

I dont't have MSVC with C++/CLI, but just on the off-chance that it works, try
"__stdcall" instead of "__cdecl" (I don't know whether the language provides
that keyword, but probably it does).

First, it just seems more correct, since those API functions are stdcall.

Second, it may be that "__cdecl" adds an underscore at the start of the name.

However, are you sure that you really need to use that DllImport mechanism?

Since I haven't used C++/CLI I can't say for sure, but I had the impression that
you could use the Windows API directly.

Cheers, & hth.,

- Alf

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