Question

I’m trying to load a hypothetical plugin with the following header:

#ifndef _DLL_H_
#define _DLL_H_

#if BUILDING_DLL
# define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */


class DLLIMPORT DllClass
{ 

  public:

    virtual ~DllClass(void);
    static DllClass* getPCFilter(); 
    virtual int Process(int a, int b);

  protected:

    DllClass();
};


#endif /* _DLL_H_ */

And my host code does:

HINSTANCE hinstDLL;
hinstDLL = LoadLibrary(L"PCFilter.dll");

if(hinstDLL)
{
    typedef DllClass*(*Factory)();
    Factory fun1;

  fun1 = (Factory)GetProcAddress(hinstDLL, "DllClass::getPCFilter");

The dll opens but the GetProcAddress is not finding the static factory method. Am I not supposed to be able to do it this way?

I’ve tried getting rid of the static method and instead, after the class declaration, doing the following:

extern "C" DLLIMPORT void* getPCFilterInstance()
{
    return (void*)new DllClass();
}

But then, when compiling the host source, the linker complains:

In function `getPCFilterInstance'::
[Linker Error] undefined reference to `_imp___ZN8DllClassC1Ev'

This I can solve by linking to the .a lib. But isn’t the idea of the DLL to not need to link at compile time?

Answer 1

You can use extern "C" statement to export your function with the same name as you’ve declared it in the code – otherwise it will get mangled by the c++ compiler