Re: Linking error in mixed code

From:

"Mark Salsbery [MVP]" <MarkSalsbery[MVP]@newsgroup.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 22 Jul 2008 09:53:58 -0700

Message-ID:

<ulb6JuB7IHA.1192@TK2MSFTNGP05.phx.gbl>

<swtbase@gmail.com> wrote in message
news:2dd7ebf1-48ce-408e-a455-752e9b43e865@2g2000hsn.googlegroups.com...

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 =
CharSet::Unicode)]
extern "C" long __cdecl SetClipboardViewer(void* hWnd);

[DllImport("user32", EntryPoint = "SetWindowLong", CharSet =
CharSet::Unicode)]
extern "C" long __cdecl SetWindowLongW(void* hWnd, int nIndex, long
dwNewLong);

[DllImport("user32", EntryPoint = "CallWindowProc", CharSet =
CharSet::Unicode)]
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
UnManagedFuncs::SetClipboardViewer((void*)this->Handle);

                               UnManagedFuncs::HookWindow((void*)this-

Handle);

}
}

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 *)" (?
HookWindow@UnManagedFuncs@@YAXPAX@Z)

What is wrong?

I'm not sure why you are compiling the DllImport stuff unmanaged.

Using .NET types for interop should make things simpler, no?

You should only need something like this (compiled MANAGED!):

[DllImport("user32.dll", CharSet = CharSet::Unicode)]
extern long SetClipboardViewer(IntPtr hWnd);

[DllImport("user32.dll", CharSet = CharSet::Unicode)]
extern long SetWindowLongW(IntPtr hWnd, int nIndex, long dwNewLong);

[DllImport("user32.dll", CharSet = CharSet::Unicode)]
extern long CallWindowProcW(IntPtr lpPrevWndFunc, IntPtr hWnd, unsigned int
uMsg, unsigned int wParam, long lParam );

Also, note the use of IntPtr instead of void* and/or long pointers.
For 53-bit compatibility, IntPtr should also be used for all those WPARAMs
and LPARAMS, but the above should work fine for 32-bit code.

Mark

--
Mark Salsbery
Microsoft MVP - Visual C++