how to export "DllCanUnloadNow" (prototypied in objbase.h) without .DEF file

[Mario Semo]

Hello,

This is not a windows api related question - even when my problems are based
on some windows standard (SDK) header files.

i want to export DllCanInloadNow (one of the COM-Server APIs) in my DLL.
The function is prototyped in objbase.h.
And this is the problem, the function is prototypied without any "export"
definition. So the question is : how to export this function without help of
external .DEF files.

Sample:

========= dll2.cpp =========
#include <windows.h>

#define X_Export __declspec(dllexport)

// BaseTyps.h
// #define STDAPI EXTERN_C HRESULT STDAPICALLTYPE
// ObjBase.h
// STDAPI DllCanUnloadNow(void);

// 1st try
//X_Export STDAPI DllCanUnloadNow() -> error (invalid order of extern "C"
and linkage, ok!)

// 2nd try
EXTERN_C X_Export HRESULT STDAPICALLTYPE DllCanUnloadNow(void)
// dll2.cpp(13) : error C2375: 'DllCanUnloadNow' : redefinition; different
linkage
// C:\Programme\Microsoft SDKs\Windows\v6.0A\include\objbase.h(854) :
see declaration of 'DllCanUnloadNow'
{
return 0;
}
=================================

cl -W4 -nologo -D__WINDOWS__ /J /LD dll2.cpp

thx for any help.

mario.

[Igor Tandetnik]

Mario Semo <mario...@Xhotmail.com> wrote:
> i want to export DllCanInloadNow (one of the COM-Server APIs) in my
> DLL. The function is prototyped in objbase.h.
> And this is the problem, the function is prototypied without any
> "export" definition. So the question is : how to export this function
> without help of external .DEF files.

You could use /EXPORT linker option, either specified in your project or
introduced in the source code via #pragma comment.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

[Mario Semo]

Igor,

>
> You could use /EXPORT linker option, either specified in your project or
> introduced in the source code via #pragma comment.

Ah, this is interesting.

So i tried:

STDAPI DllCanUnloadNow()
{
return 0;
}

#pragma comment(linker, "/EXPORT:DllCanUnloadNow")

since the documentation to /EXPORTS says:

Do not specify the decorated form of C identifiers that are declared __cdecl
or __stdcall.

But this results in:

dll2.obj : warning LNK4104: export of symbol 'DllCanUnloadNow' should be
PRIVATE
Creating library dll2.lib and object dll2.exp
dll2.exp : error LNK2001: unresolved external symbol DllCanUnloadNow
dll2.dll : fatal error LNK1120: 1 unresolved externals

mh?

then i tried the decorated form:

#pragma comment(linker, "/EXPORT:_DllCanUnloadNow@0")

and now i looks as it is ok.

comments?

thx a lot for your help!

mario

[Ben Voigt [C++ MVP]]

But now the name is wrong, when COM looks for "DllCanUnloadNow" with
GetProcAddress, it won't find it.

[Mario Semo]

Ben,

"Ben Voigt [C++ MVP]" <r...@nospam.nospam> schrieb im Newsbeitrag
news:OLt6fjUh...@TK2MSFTNGP04.phx.gbl...

>>
>> #pragma comment(linker, "/EXPORT:DllCanUnloadNow")
>>
>>

>> #pragma comment(linker, "/EXPORT:_DllCanUnloadNow@0")
>>

> But now the name is wrong, when COM looks for "DllCanUnloadNow" with

> GetProcAddress, it won't find it.
>

But
a) extern "C" __stdcall functions are always mangeled (decorated) by VC++
and the function is prototyped this way.
b) what whould be the correct way to export?
c) when i ignore the prototype in the windows header file and change it to

extern "C" __declspec(dllexport) unsigned long __stdcall DllCanUnloadNow()
/* use unsigned long instead of HRESULT so i do not need to include
windows.h */

and implement this function, then i have 2 binaries based on 2 different
sources:

=== dll1.cpp ===
#include <windows.h>
STDAPI DllCanUnloadNow()
{ return 0; }

//#pragma comment(linker, "/EXPORT:DllCanUnloadNow") // this will give a
linker error since __stdcall functions are decorated.

#pragma comment(linker, "/EXPORT:_DllCanUnloadNow@0")

=================

===== dll2.cpp =======
extern "C" __declspec(dllexport) unsigned long __stdcall DllCanUnloadNow()
/* use unsigned long instead of HRESULT so i do not need to include
windows.h */
{
return 0;
}
==================

and dumpbin /Exports dll.dll
(for both dlls)

gives exactly the same result!

1 0 00001005 _DllCanUnloadNow@0 = @ILT+0(_DllCanUnloadNow@0)

So, the question is : how to implement DllCanUnloadNow with VC++ (without
.DEF file)

thx,
mario.

[Ben Voigt [C++ MVP]]

> and dumpbin /Exports dll.dll
> (for both dlls)
>
> gives exactly the same result!
>
> 1 0 00001005 _DllCanUnloadNow@0 =
> @ILT+0(_DllCanUnloadNow@0)
> So, the question is : how to implement DllCanUnloadNow with VC++
> (without .DEF file)

Only a DEF file lets you control the name in the exports table.

>
> thx,
> mario.