Version 4 of Building Tcl DLL's for Windows

Using Microsoft Visual C++ 6

Create a new win32 dynamic link library project and call it something nice, like tcldemo. This is going to be our package name too.
Select an 'Empty DLL' on the next dialog.
Before you get going, make sure you have told Visual Studio about the Tcl headers and libraries. To do this, open Tools->Options->Directories and give the Tcl include directory in the includes box and the libraries in the libraries box.
Open up the Porject settings menu item for your new project and go to the C++ tab. Add USE_TCL_STUBS to the list of defined symbols and in the Link tab prepend tclstub83.lib to the list of libraries. (Adust the numerical suffix for your version of tcl).
Now we can write some code. Create a new C++ source file, called tcldemo.cpp and paste in the code below.
Build it. Ignore the whining about MSCVRT conflicts. You now have a DLL in either Debug/Release.
Fire up tclsh or better tkcon from the Debug or Release subdirectory under your project and issue

  load tcldemo.dll Tcldemo
  set tcldemo_version
  package require Tcldemo

You should get 0.1 printed twice!

Using mingw32 GNU C++

If you don't happen to have a copy of Microsoft's compiler then you can get a copy of GNU C compiled for the win32 platform. The mingw32 project is the minimal approach which uses only the native libraries and so doesn't support unix porting much - see http://sourceforge.net/projects/mingw32 for the releases.

Create a .cpp or .cc file with the code below using your favourite editor. (eg: emacs)
Create a tcldemo.def file with the following lines:

 EXPORTS
 Tcldemo_Init
 Tcldemo_SafeInit

Compile the code:

 g++ -Wall -g -Ii:/opt/Tcl/include -c tcldemo.cpp -o tcldemo.o

Link the code. If you are using a standard distribution such as ActiveTcl then see How to create mingw32 libraries from DLLs:

 dllwrap --driver-name g++ -def tcldemo.def -o tcldemo.dll tcldemo.o -Li:/opt/Tcl/lib -ltcl83 -lm

Voila: you now have a tcldemo.dll. Test as above.

The code:

 #include <windows.h>
 #include <tcl.h>

 #ifndef DECLSPEC_EXPORT
 #define DECLSPEC_EXPORT __declspec(dllexport)
 #endif // DECLSPEC_EXPORT

 BOOL APIENTRY
 DllMain(HANDLE hModule, DWORD dwReason, LPVOID lpReserved)
 {
     return TRUE;
 }

 EXTERN_C int DECLSPEC_EXPORT
 Tcldemo_Init(Tcl_Interp* interp)
 {
 #ifdef USE_TCL_STUBS
     Tcl_InitStubs(interp, "8.3", 0);
 #endif
     Tcl_Obj *version = Tcl_SetVar2Ex(interp, "tcldemo_version", NULL,
                                      Tcl_NewDoubleObj(0.1), TCL_LEAVE_ERR_MSG);
     if (version == NULL)
         return TCL_ERROR;
     int r = Tcl_PkgProvide(interp, "Tcldemo", Tcl_GetString(version));

     // Call Tcl_CreateObjCommand etc.

     return r;
 }

 EXTERN_C int DECLSPEC_EXPORT
 Tcldemo_SafeInit(Tcl_Interp* interp)
 {
     // We don't need to be specially safe so...
     return Tcldemo_Init(interp);
 }

This excellent piece of work was created and put here by Pat Thoyts. Thanks Pat!