Robert Giesecke's Unmanaged Exports

Question

I'm trying to get an DllExport from vb.net to unmanaged c++ working.

I'm using Robert Giesecke's Unmanaged Exports with Visual Studio 2012 and tried to follow this very helpful hints. I copy the dlls from the .Net project by an post build action in the directory where my *.cpp and *.h files reside.

I checked my dll with dumpbin /EXPORTS Nugget.Discovery.dll and it tells me that there are exports:

File Type: DLL
Section contains the following exports for \Nugget.Discovery.dll
00000000 characteristics
52554A05 time date stamp Wed Oct 09 14:20:21 2013
    0.00 version
       0 ordinal base
       2 number of functions
       2 number of names
ordinal hint RVA      name
      0    0 0000532E StartAnnouncing
      1    1 0000533E StopAnnouncing
Summary
    2000 .reloc
    4000 .rsrc
    2000 .sdata
    4000 .text

But if I try to import it in the cpp file with

#import "Nugget.Discovery.dll" 
   void StartAnnouncing(int serial);

I get one IntelliSense error and one error after I try to compile:

IntelliSense: cannot open source file "Debug/Nugget.Discovery.tlh"
error C1083: Cannot open type library file: 'nugget.discovery.dll': Fehler beim Laden der Typbibliothek/DLL.

Any idea what I'm doing wrong?

Best regards! Stefan

Answer 1

Ok, thanks to Hans Passant I came to this solution:

This is my code on the managed side:

Imports System.Runtime.InteropServices
Imports RGiesecke.DllExport

Public NotInheritable Class Beacon

Private Sub New()
End Sub

Private Shared _nuggetAnnouncement As NuggetAnnouncement

' ReSharper disable UnusedMember.Local
''' <remarks>Cannot be called from managed code!</remarks>
<DllExport("StartAnnouncing", CallingConvention.StdCall)>
Private Shared Sub StartAnnouncingNative(serial As Integer)
    StartAnnouncing(serial)
End Sub

''' <remarks>Cannot be called from managed code!</remarks>
<DllExport("Test", CallingConvention.StdCall)>
Private Shared Function TestNative() As Integer
    Return Test()
End Function
' ReSharper restore UnusedMember.Local

Public Shared Sub StartAnnouncing(serial As Integer)
    'do something
End Sub

Public Shared Function Test() As Integer
    Return 42
End Function

End Class

Interesting is, that I cannot call functions that are marked with <DllExport> from managed code (even if they are Public).

And this is the code on the native side:

typedef void (CALLBACK* StartAnnouncingType)(int);
typedef int (CALLBACK* TestType)(void);

int _tmain(int argc, _TCHAR* argv[])
{
HINSTANCE dllHandle = NULL;   
StartAnnouncingType  StartAnnouncingPtr = NULL;
TestType TestPtr = NULL;
wchar_t dllNameWide[64];
int size = mbstowcs(dllNameWide, "Nugget.Discovery.dll", sizeof(dllNameWide));
dllHandle = LoadLibrary(dllNameWide);
if (NULL != dllHandle) 
{ 
  //Get pointer to our function using GetProcAddress:
  StartAnnouncingPtr = (StartAnnouncingType)GetProcAddress(dllHandle,"StartAnnouncing");
  TestPtr = (TestType)GetProcAddress(dllHandle,"Test");
  int test;
  if (NULL != TestPtr) test = TestPtr();
  int serial = 1;
  if (NULL != StartAnnouncingPtr) StartAnnouncingPtr(1);
  //Free the library:
  FreeLibrary(dllHandle);    
}
}

Are there any other better solutions?

Ciao! Stefan

Answer 2

As part of DllExport, a .lib file is generated. You can use that to use the normal C++ linker instead of LoadLibrary/GetProcAddress.

Starting from the managed code you posted, on the native side:

extern CALLBACK void StartAnnouncingType(int serial);
extern CALLBACK int TestType(void);

int _tmain(int argc, _TCHAR* argv[])
{
    int test = TestPtr();
    StartAnnouncingPtr(1);
}

In the settings of you unmanaged project, add Nugget.Discovery.lib to the project properties: Configuration Properties->Linker->Input. And copy the Nugget.Discovery.dll to the output directory.