writing to a shared variable in a dll

**cloudy** · 07-17-2007

Hi all,

I have a dll file which im loading using LoadLibrary. I wish to pass the dll my windows HWND by including the dll header file in my exe and using decl(dllimport) to assign to it. Problem is that i'm getting the warning.

c4273 g_TargetHwnd inconsistent dll linkage

This is my code:

Dll Header File:

Code:

#if !defined MYDLL_DLL_H
#define MYDLL_DLL_H
 
  #ifdef MYDLL_DLL_EXPORTS
  #define MYDLL_DLL_API __declspec(dllexport)
  #else
  #define MYDLL_DLL_API __declspec(dllimport)
  #endif
 
 extern MYDLL_DLL_API HWND g_TargetHwnd;

#endif // !defined(MYDLL_DLL_H)

Now this is the code in the cpp file which is causing me the headache:

Code:

#pragma data_seg (".shared")
HWND	g_TargetHwnd = 0;
#pragma data_seg ()

#pragma comment(linker,"/SECTION:.shared,RWS")

Now for some reason I keep getting that warning. I have no idea why because i have used this technique before fine.

Any ideas?

**abachler** · 07-17-2007

Originally Posted by cloudy

Code:

#pragma data_seg (".shared")
extern HWND    g_TargetHwnd = 0;
#pragma data_seg ()
 
#pragma comment(linker,"/SECTION:.shared,RWS")

It wasnt really clear whether the cpp includes the header file, but im assuming it does. Better yet, just remove that section, since if you are declaring it as extern, you dont need to redeclare the variable in the cpp proper

**cloudy** · 07-17-2007

Thanks for the reply

When i add the extern inside the #pragma shared block it makes no difference.

If i completely remove the #pragma shared stuff i get a link error saying:

unresolved external symbol __declspec(dllimport) struct HWND__ * g_TargetHwnd

**abachler** · 07-17-2007

extern __declspec(dllimport)HWND g_TargetHwnd;

never redefine an external variable by assignment. Is there some reason why you cant use the lib from the DLL project? is it a cross compiler project, or is the DLL from a 3rd party?

**cloudy** · 07-17-2007

Thanks for your help, i manged to get rid of the warning but it still isnt working.

I belive the problem is either due to the DLL not exporting the variable correctly or the app not importing it, maybe both.

I changed the dll to not use __declspec(dllexport)and to export it using a module definition file like so,

EXPORTS
g_TargetHwnd

The app does the following:

Code:

__declspec(dllimport) HWND g_TargetHwnd

Everything compiles fine, but during runtime when the app does this:

g_TargetHwnd = myHwnd ;

the g_TargetHwnd in the dll file doesnt get updated, it remains 0.

Is there something i should know about using __declspec(dllimport), like an option i need to turn on in the project settings or anything?

Thanks again mate.

Edit:
On Msdn it says that to use __declspec(dllimport) i must be including the library. So i take it that just means to add MyDll.lib to the AdditionalDependencies in project setttings-> Linker->Input?

Thread: writing to a shared variable in a dll

Thread Tools

Search Thread

Display

writing to a shared variable in a dll

Similar Threads

Query related to posting message from a regular dll to Client Application?

DLL compiling question

DLL and std::string woes!

mfc as shared dll

Exporting Object Hierarchies from a DLL