Calling D from C++

[Loopback]

On 2011-07-17 22:51, Johann MacDonagh wrote:
> On 7/17/2011 3:53 PM, Loopback wrote:
>> On 2011-07-17 21:45, Loopback wrote:
>>> Hello!
>>>
>>> As of my understanding you can write usable c libraries in D by using
>>> extern(C). The problem is that I haven't found any other threads asking
>>> the same question about C++ (since extern for c++ exists as well). So
>>> I have two questions, is it possible to write a dll in D usable in c++
>>> code, and if the answer is yes, are there any restrictions?
>>>
>>> Am I forced to use explicit memory handling, or can this be handled by
>>> the garbage collection internally by the dll etc?
>>
>> Sorry for mentioning this a bit late but noticed this now;
>> http://www.digitalmars.com/d/2.0/cpp_interface.html
>>
>> Although if someone has own experiences or something interesting to say
>> about the matter, please do.
>
> I think you're going to be better off defining your D routines as
> extern(C) and then defining the C++ headers as __cdecl (for Windows of
> course). C++ can, of course, link against libraries using cdecl.
>
> If you write your D DLL with the normal DllEntry (this came from VisualD):
>
> import std.c.windows.windows;
> import core.dll_helper;
>
> __gshared HINSTANCE g_hInst;
>
> extern (Windows)
> BOOL DllMain(HINSTANCE hInstance, ULONG ulReason, LPVOID pvReserved)
> {
> switch (ulReason)
> {
> case DLL_PROCESS_ATTACH:
> g_hInst = hInstance;
> dll_process_attach( hInstance, true );
> break;
>
> case DLL_PROCESS_DETACH:
> dll_process_detach( hInstance, true );
> break;
>
> case DLL_THREAD_ATTACH:
> dll_thread_attach( true, true );
> break;
>
> case DLL_THREAD_DETACH:
> dll_thread_detach( true, true );
> break;
> }
> return true;
> }
>
> Then as soon as your DLL is loaded the D runtime will start. Any memory
> allocated in the D DLL will be garbage collected as you'd imagine.
> Obviously, it's not going to free any memory allocated in your C++ code ;)
>
Thank you for your reply!

I've written a C++ wrapper which communicates with D function but I have
stumbled upon an error. With the code win32 DLL code on the digitalmars
webpage (and yours) I receive linker errors:

  Error 42: Symbol Undefined 
_D4core10dll_helper18dll_process_detachFT4core3sys7w
indows7windows6HANDLEbZv

  Error 42: Symbol Undefined 
_D4core10dll_helper18dll_process_attachFT4core3sys7w
indows7windows6HANDLEbPvPvPvPiZb

  Error 42: Symbol Undefined _D4core13thread_helper12__ModuleInfoZ

 From my experience ModuleInfo undefined is often caused by not supplying
a required source file to the linker, but since I only use functions
from the library, I shouldn't be required to do that. Any tips?