CODEWITHSUNDEEP
c++visual-studiodllshared-librariesunresolved-external
balint.miklos
balint.miklos

Reputation: 1887

Static class members in shared library

I have a class like

class K {
  static int a;
  static int b;
}

I would like to create a shared library (dll) containing this class K. In a cpp file compliled in the library I call

int K::a = 0;
int K::b = 0;

to instantiate the static variables. The dll does compile without errors, but when I use the library, I get the unresolved external symbol error for the members K::a and K::b. In the main program where I want to use it, I include the same header with the declaration of the class K, the only difference is that for the library I use class __declspec( dllexport ) K { ... } and for the main program class K { ... }

Probably I am doing more than one mistake so my questions would be, how can I

PS. I use Visual Studio 2008...

Upvotes: 3

Views: 2588

Answers (2)

balint.miklos
balint.miklos

Reputation: 1887

One should use __declspec( dllimport ) in the header in the main application.

So here is the solution. The header file (included in both the library and the main application) is:

#ifdef COMPILE_DLL
#define DLL_SPEC __declspec( dllexport )
#else
#define DLL_SPEC __declspec( dllimport )
#endif

class DLL_SPEC K {
   static int a;
   static int b;
}

The cpp file in the library contains:

int K::a = 0;
int K::b = 0;

To compile the library one has to define the macro COMPILE_DLL, for the main application it shouldn't be defined.

Upvotes: 1

Kieveli
Kieveli

Reputation: 11075

Link the libarary statically instead of dynamically.

Or add a global function in the DLL that returns the values.

Upvotes: 0

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