Problem on Linking extern variables

[Mani1978]

Hi,
I have problem on linking an extern variable.

My code is look like as follows.

My dll contains the following code

DllTest.h
-----------

#include <iostream>

namespace Test
{
__declspec(dllexport) extern int* i;
}

DllTest.cpp
--------------

#include "DllTest.h"

namespace Test
{
__declspec(dllexport) int *i = NULL;
}

If i make a dll with above code it is done.
When i am linking this dll with my Test program it gives the error
error LNK2001: unresolved external symbol "int * Test::i" (?i@Test@@3PAHA)

My Test Program for this dll is

#include <DllTest.h>

void main()
{
if (Test::i == NULL)
{
printf("Null");
}
else
{
printf("Not Null");
}
}

If anybody gives solution i am very much happy......
thanks in advance

Regards
Manikandan

[Richard.J]

checkout this thread
http://www.codeguru.com/forum/showth...hreadid=229800

[vinodp]

The way ur using ur variable for that u need to have ur DLL should be implicitaly link.
How r u linking ur DLL? Is it implicit linking?
See MSDN article here

If ur linking ur DLL implicitaly then name mangling might be issue.
when ur trying to export from a DLL use extern "C" so that u can use it with diff. kind of name mangling schemes.

rgds,
Vinod

[Mani1978]

Hi Richard,
I didn't understand how it will solve my problem from the thread given by you. Please can you explain.

[Mani1978]

Hi Vinod,
I tried with extern "C", still i am getting the same error.

Yes, I am using implicit linking.
Can u solve this problem?

thanks
Regards
Manikandan

[rxbagain]

The problem is that the variable is always defined as dllexport even when it should be dllimport or no modifier at all in the app that uses the dll. It's often better to add macros that will make your life easier

DllTest.h
#ifdef _MY_DLL_BUILDING
#define DLLEXPORT __declspec(dllexport)
#else
#define DLLEXPORT __declspec(dllimport)
#endif

#include <iostream>

namespace Test
{
   extern DLLEXPORT extern int* i;
}


DllTest.cpp
#ifndef _MY_DLL_BUILDING
   #define _MY_DLL_BUILDING
#endif
#include "DllTest.h"

namespace Test
{
   DLLEXPORT int *i = NULL;
}


// test app
#include <DllTest.h>
#pragma comment (lib, "DllTest.lib")

void main()
{
   if (Test::i == NULL) printf("Null"); else printf("Not Null");
}

Hope it will help you

[Mani1978]

Hi,
Thanks for all.........
The problem is solved. It is actually because of export and import.
Thanks for all ur help.

Regards
Manikandan