Your DLL project should produce a LIB file when it compiles. Go to your DLL project properties, under Linker->Advanced->Import library there should be something along the lines of $(TargetName).lib (add it if not). Go to your joystick project properties under Linker->Input and make sure that library is included under 'additional dependencies'. You might also need specify the directory the lib file is in under Linker->General->Additional Library Dependencies.

Did you rebuild the plugin project (with MYPLUGIN_EXPORTS defined) once you added the header file and relevant function code? THAT is the lib file you need, not some random one you found in a directory. You use those kind of libs to access functions written by other people in DLLs you don't have code for.

And yes, in your joystick project #define PLUGINFN __declspec(dllexport) should be grayed out and PLUGINFN __declspec(dllimport) should be defined because you're not exporting those functions so another program can use them, you're importing them so you can use them.

Here's a very simple project:

MyPlugin.h (included in both your joystick project and DLL)

#pragma once#ifdef MYPLUGIN_EXPORTS#define PLUGINFN __declspec(dllexport)#else#define PLUGINFN __declspec(dllimport)#endifPLUGINFN	int		Plugin_GetValue();PLUGINFN	void	Plugin_SetValue(int v);

MyPlugin.cpp (main piece of your DLL):

// MyPlugin.cpp : Defines the entry point for the DLL application.//#include "stdafx.h"#define MYPLUGIN_EXPORTS#include "../IPC_TEST/MyPlugin.h"			// include the header we wrote before, but now we'll use it for exports#pragma data_seg (".SHARED")	int		g_PLUGIN_VALUE = 0;#pragma data_seg()#pragma comment(linker, "/section:.SHARED,RWS")BOOL APIENTRY DllMain( HMODULE hModule,                       DWORD  ul_reason_for_call,                       LPVOID lpReserved					 ){	return TRUE;}// Define plugin functionsPLUGINFN int		Plugin_GetValue() { return g_PLUGIN_VALUE; }PLUGINFN void		Plugin_SetValue(int v) { g_PLUGIN_VALUE = v; }

Now you compile that and you get a LIB file. Using your header in conjunction with this LIB file will allow you to access those plugin functions.

Test Project:

#include "stdafx.h"#include "MyPlugin.h"				// <-- header file that describes what our Plugin exports#include <iostream>int _tmain(int argc, _TCHAR* argv[]) {	if (Plugin_GetValue() == 10) {		Plugin_SetValue(20);	} else Plugin_SetValue(10);	using std::wcout;	using std::wcin;	wchar_t input = '\0';	while (true) {		wcout << "Current value of MyPlugin: " << Plugin_GetValue() << std::endl;		wcout << "Press a key to check again, or q/Q to quit\n";		wcin >> input;		if ((input == 'q') || (input == 'Q'))			break;	}	return 0;}

Make sure your test project is built with the LIB file produced by the above dll project linked.

Now we'll share that plugin value across two separate processes. Run an instance of the EXE you just created. It'll show you the current value, 10. Press any char (other than q of course) and press enter to check the value again. No matter how many times you check it, it's 10.

Now open another instance of the program. It shows the value as 20, proving that even though it's got a whole new copy of the DLL in memory, it's got a hold of the data in the first program. Go back to the first program and have it check the value again to convince yourself that information really is crossing process boundaries.

Make sure MYPLUGIN_EXPORTS is not defined in your joystick project, only in the DLL project.

Could you post your project somewhere?

Multithread shouldn't be an issue. It's when two threads try to write to memory at the same time that bad stuff starts to happen, and that's pretty easily solved with a mutex or similar.

Hopefully SDL does the trick for you