How to fix _DllMain@12 already defined error?

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C++

I am creating my own DLL which make use of Detours 2.1 of MS Research.
But I got these errors:

detours.lib(detoured.obj) : error LNK2005: _DllMain@12 already defined in SampleDLL.obj
Debug/SampleDLL.dll : fatal error LNK1169: one or more multiply defined symbols found

I think its because, detoured.cpp contains BOOL WINAPI DllMain(...) when I compiled it using nmake

How should I fix this problem. I saw in some other forums, that it should be removed. But is it okay have a DLL without it?

Here's the code regarding the DLL I want to make (The code isn't mine, just copied it on a forum. It actually tries to hook to DrawTextW):

// SampleDLL.cpp code

int (WINAPI * Real_DrawText)(HDC a0, LPCWSTR a1, int a2, LPRECT a3, UINT a4) = DrawTextW;

// Our custom version of DrawText
int WINAPI Mine_DrawText(HDC hdc, LPCWSTR text,  int nCount, LPRECT lpRect, UINT uOptions)
{
    TRACE("=== %s", text, " ===");
    int rv = Real_DrawText(hdc, text, nCount, lpRect, uOptions);
    return rv;
}

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
					 )
{
    switch (ul_reason_for_call)
    {
        case DLL_PROCESS_ATTACH:
            
            DetourTransactionBegin(); 
            DetourUpdateThread(GetCurrentThread());
            DetourAttach(&(PVOID&)Real_DrawText, Mine_DrawText); // <- magic
            DetourTransactionCommit();
            break;

        case DLL_PROCESS_DETACH:
            DetourTransactionBegin(); 
            DetourUpdateThread(GetCurrentThread());
            DetourDetach(&(PVOID&)Real_DrawText, Mine_DrawText);
            DetourTransactionCommit();
            break;
    }
    return TRUE;
}