How can i set an entrypoint for a dll

First i thought entry point in dlls开发者_StackOverflow社区 DLLMain but then when i try to import it in C# i get an error that entrypoint wasn't found Here is my code:

#include <Windows.h>

int Test(int x,int y)
{
    return x+y;
}

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        MessageBox(0,L"Test",L"From unmanaged dll",0);
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
} 

How can i set an entry point for my dll? And if you dont mind can you give me little explanation about entry point?

Like do i have to set import the same dll again and changing the entry point so i can use other functions in same dll? thanks in advance.

In your example, it seems you intend Test() to be an entry point however you aren't exporting it. Even if you begin exporting it, it might not work properly with C++ name "decoration" (mangling). I'd suggest redefining your function as:

extern "C" __declspec(dllexport) int Test(int x,int y)

The extern "C" component will remove C++ name mangling. The __declspec(dllexport) component exports the symbol.

See http://zone.ni.com/devzone/cda/tut/p/id/3056 for more detail.

Edit: You can add as many entry points as you like in this manner. Calling code merely must know the name of the symbol to retrieve (and if you're creating a static .lib, that takes care of it for you).