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Asked: 2026-05-14T01:44:38+00:00

I have a DLL which contains a class with static members . I use

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I have a DLL which contains a class with static members. I use __declspec(dllexport) in order to make use of this class’s methods. But when I link it to another project and try to compile it, I get “unresolved external symbol” errors for the static data.

e.g.
In DLL, Test.h

class __declspec(dllexport) Test{
protected:
    static int d;
public:
    static void m(){int x = a;}
}

In DLL, Test.cpp

#include "Test.h"

int Test::d;

In the application which uses Test, I call m().

I also tried using __declspec(dllexport) for each method separately but I still get the same link errors for the static members.

If I check the DLL (the .lib) using dumpbin, I could see that the symbols have been exported.

For instance, the app gives the following error at link time:

1>Main.obj : error LNK2001: unresolved external symbol "protected: static int CalcEngine::i_MatrixRow" (?i_MatrixRow@CalcEngine@@1HA)

But the dumpbin of the .lib contains:

Version      : 0
  Machine      : 14C (x86)
  TimeDateStamp: 4BA3611A Fri Mar 19 17:03:46 2010
  SizeOfData   : 0000002C
  DLL name     : CalcEngine.dll
  Symbol name  : ?i_MatrixRow@CalcEngine@@1HA (protected: static int CalcEngine::i_MatrixRow)
  Type         : data
  Name type    : name
  Hint         : 31
  Name         : ?i_MatrixRow@CalcEngine@@1HA

I can’t figure out how to solve this. What am I doing wrong? How can I get over these errors?

P.S. The code was originally developed for Linux and the .so/binary combination works without a problem

EDIT: In the given case, the static variables are not directly referred by the application but the method is inlined since it’s in the header. I was able to resolve the link errors by moving the methods to the .cpp file.

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1 Answer

  1. Editorial Team

    In this thread at cprogramming.com it is suggested that a static variable is local to the dll and not exported.

    Summary of discussion below

    The static member is not accessed directly by code in the calling application, only through member functions of the class in the dll. However there are several inline functions accessing the static member. Those functions will be inline expanded into the calling applications code makeing the calling application access the static member directly. That will violate the finding referenced above that static variables are local to the dll and cannot be referenced from the calling application.

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