Mail Archives: cygwin/2004/08/27/16:36:44
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 _DllMain AT 12
67481000 T _DllMainCRTStartup AT 12
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++.
Oliver
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