writing a dll in visual studio 2008

I am trying to write a dll file with visual studio 2008 and i am having a problem. here is the source code for the dll:

Code:

---

#include <windows.h>
#include <winsock.h>

BOOL WINAPI DllMain (HANDLE hModule, DWORD dwFunction, LPVOID lpNot)
{
        return TRUE;
}

long _stdcall add_num (long a, long b)
{
        return ((long)(a+b));
}

---

i cant seem to get this dll function to work though. I dont have any build errors or anything but i cant get the dll to load into my liberty basic project for some reason i keep getting a dll load error. I know that i am supposed to use a .def file but i cant seem to figure out how to use it with visual studio 2008. Im really messed up here.

you are not exporting it. Add a __declspec(dllexport) compile directive to your functions signature. Also for better header reuse (since it will also be required to call your exported functions), you usually see something like this done.

Code:

---

#ifdef DLL_EXPORT
#define MY_API __declspec(dllexport)
#else //DLL_EXPORT
#define MY_API __declspec(dllimport)
#endif //!DLL_EXPORT

---

??? Ok, now im really confused. i changed my function to the call you said to, but it still wont work. I'm really lost. maybe i'll try to read up on it tomorrow some more?

Are you placing the dll in the same directory as your executable? What exactly is the error?

To clarify what valaris said.

A DLL must EXPORT a function (for apps to use).
To use a DLL function you must IMPORT it.

This code snippet allows you to use the same header file in the DLL and the app (avoiding any issues from maintaining diff import/export header files).

Code:

---

#ifdef DLL_EXPORT
#define MY_API __declspec(dllexport)
#else //DLL_EXPORT
#define MY_API __declspec(dllimport)
#endif //!DLL_EXPORT

---

This code is placed at the top of the DLL header file (before function declarations).
Change the function declaration to;

DLL_EXPORT int MyFunc(int iInput);

In the DLL c./.cpp file you first #define DLL_EXPORT and then include the DLL header.

In the APP you only include the header (and do not define DLL_EXPORT).