On Fri, 27 Aug 2004, Oliver wrote:
> Igor Pechtchanski <pechtcha <at> cs.nyu.edu> writes:
>
> > The newer versions of gcc apparently allow you to link directly to a .dll
> > file. The .def and .a are needed for older versions of gcc, and possibly
> > for some other tools.
> >
> > [...]
> >
> > The reason you want an 'extern "C"' for DLL functions in general is that
> > g++ and the Windows C++ compilers (notably VC++) use different name
> > munging schemes, so a DLL built with C++ symbols won't be usable from
> > other applications that try to call those functions. The reason you want
> > it for DllMain is that the Windows loader will be looking for the unmunged
> > name "DllMain". Are you sure that it's really invoked when the DLL is
> > loaded?
>
> Actually I found something quite interesting on a "Tcl extensions in
> Windows" wiki website, where a poster says that DllMain, __decl...
> import export, windows.h etc are no longer needed with g++. Sure enough,
> the following example works:
>
> 1) create a dll.h file that contains a class definition, just like you
> would on Unix (i.e. no __decl... macros, no extern etc)
> 2) create a dll.cc file that contains some of your class definition methods
> 3) then create the dll with
>
> g++ -c dll.o
> g++ -shared dll.o -otestdll.dll
>
> 4) create a testMain.cc file with a main() that #includes dll.h and uses
> some things defined in dll.cc
> 5) build with
>
> g++ -o testMain testMain.cc -L. -ltestdll
>
> 6) run testMain.exe to make sure it works
>
> Note that extern, gcc, import/export macros and declarations, DllMain
> etc were NOT needed. Gcc seems to export everything, like it would on
> *nix (except, presumably, functions declared static and things in
> anonymous namespace -- exercise left to the reader ;).
>
> You can tell the linker to generate a .def file by adding "-Wl,--output-
> def=testdll.def" when creating the testdll.dll. This shows all symbols
> exported. Running nm on testdll.dll also shows
>
> 67488220 T [EMAIL PROTECTED]
> 67481000 T [EMAIL PROTECTED]
>
> which means that gcc auto-generated it, and did not mangle for C++ use.
>
> Does anyone know if testdll.dll, created this way, would be linkable from a
> VC++ program? I don't have access to VC++.
First off, yes, a DllMain will be generated automatically if you don't
provide it. That still doesn't address the issue of whether you should
declare it as 'extern "C"' when you *do* provide it. It seems that
APIENTRY is enough.
Secondly, the resultant DLL will be linkable from a VC++ program, but the
C++ functions in it will not be accessible from code compiled with VC++.
Igor
--
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