Function pointers from DLL [modified]

[Michael Siroen]

I was busy creating a Dll for some basic game engine (just for myself) For the input, I would like to have some general function pointers inside my dll which I want to be able to reference to other functions from code based upon my exe file. just like this: on_a = function_to_do_on_A; on_esc = function_to_do_on_Esc; where on_a comes from the dll and the function_to_do_on_A comes from the application. this is my code: Dll: .h #define ENGINE_EXPORTS #ifdef ENGINE_EXPORTS #define ENGINE_API __declspec(dllexport) #else #define ENGINE_API __declspec(dllimport) #endif .cpp namespace Engine { namespace Input { ENGINE_API void (*on_a)(void); ENGINE_API void (*on_b)(void); ENGINE_API void (*on_c)(void); } } Exe: .cpp void FuncA(void) { MessageBox(NULL, L"FuncA called!", L"NOTIFICATION!", MB_OK); return; } int main() { Engine::Input::on_a = &FuncA; return 0; } errors on_a is not a member of Engine::Input on_a undeclared identifier -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Exe: .cpp int main() { { using namespace Engine::Input; on_a = &FuncA; } return 0; } errors on_a undeclared identifier -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- .h namespace Engine { namespace Input { extern ENGINE_API void(*on_a)(void); } } error LNK2001: unresolved external symbol "void (__cdecl* Engine::Input::on_a)(void)" (?on_a@Input@Engine@@3P6AXXZA) What am I doing wrong? Why is my function pointer not being exported? And how to fix this problem? Many thanks in advance. ps. I am using VS2008

modified on Sunday, April 27, 2008 4:19 PM

[Mark Salsbery]

Are you linking the exe to the import library (.lib) created by the DLL build? Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Michael Siroen]

yes as follows.. #include "..\Engine\Engine.h" #if defined(DEBUG) | defined(_DEBUG) #define USE_DEBUG_ENGINE #endif #ifdef USE_DEBUG_ENGINE #pragma comment(lib, "..\\Debug\\Engine.lib") #else #pragma comment(lib, "..\\Release\\Engine.lib") #endif normal functions (and classes) declared within the namespace are working properly for instance: int Height = Engine::GetHeight(); returns the proper value

[Mark Salsbery]

The first version of your EXE code works for me as long as that last header file code is included in the EXE cpp file.

Exe:
.cpp

namespace Engine
{
namespace Input
{
__declspec(dllimport) void (*on_a)(void);
}
}

void FuncA(void)
{
MessageBox(NULL, L"FuncA called!", L"NOTIFICATION!", MB_OK);
return;
}

int main()
{
Engine::Input::on_a = &FuncA;
return 0;
}

Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Ozer Karaagac]

DllFile.h :

#ifdef ENGINE_EXPORTS
#define ENGINE_API __declspec(dllexport)
#else
#define ENGINE_API __declspec(dllimport)
#endif

namespace Engine
{
  namespace Input
  {
    ENGINE_API void (*on_a)(void);
    ENGINE_API void (*on_b)(void);
    ENGINE_API void (*on_c)(void);
  }
}

DllFile.cpp :

#define ENGINE_EXPORTS
#include "DllFile.h"

ExeFile.cpp :

#include "DllFile.h"

int main()
{
  Engine::Input::on_a = &FuncA;
  return 0;
}

[Michael Siroen]

The namespace Engine and it's 'member'- namespace Input are within the Dll file.. This means that the declaration is within the Dll file: ENGINE_API void (*on_a)(void); if I put the following code above the main function of mine: namespace Engine { namespace Input { __declspec(dllimport) void (*on_a)(void); }} I get the following warning: warning C4273: 'Engine::Input::on_a' : inconsistent dll linkage followed up with an error: error C3861: 'on_a': identifier not found

[Michael Siroen]

thanks, that already helped a lot.. (the DllCpp was the problem, #define over there instead above the header..) Since multiple header files all include this one (Engine.h), I get several (7) Errors Error LNK2005: "void (__cdecl* Engine::Input::on_a)(void)" (?on_a@Input@Engine@@3P6AXXZA) already defined in Engine.obj LuaScriptor.obj But I think I can get around that problem, or just by simply putting everything inside a single header and source file. Thanks to all for the support and the quick help :) EDIT: Fixed all (Copy everything to Engine.cpp and Engine.h), thanks

modified on Sunday, April 27, 2008 6:10 PM