C++ – error LNK2005: _DllMain@12 already defined in MSVCRT.lib

clinkervisual c++

I am getting this linker error.

mfcs80.lib(dllmodul.obj) : error LNK2005: _DllMain@12 already defined in MSVCRT.lib(dllmain.obj)

Please tell me the correct way of eliminating this bug. I read solution on microsoft support site about this bug but it didnt helped much.

I am using VS 2005 with Platform SDK

Best Answer

I had the same error message, but none of the answers here solved it for me. So if you Encounter that Problem when creating a DLL Project that uses MFC, it can be resolved by entering the following line:

extern "C" { int _afxForceUSRDLL; }

to the cpp file where DllMain is defined. Then your own DllMain implementation is used, rather than the one from dllmain.obj.

When we try to use MFC library, we surely will include afx.h directly or indirectly, then MFC(afx.h) tell the linker to find the symbol of __afxForceUSRDLL and put that object which contains __afxForceUSRDLL into the program, so linker searches and puts dllmodule.obj into our program, because __afxForceUSRDLL is defined in dllmodule.cpp.

That’s the common scenario. When we want to use our own DllMain in a mfc dll project, linker complains that there are two DllMain, one in our code, one in Dllmodule.obj.

So we need to tell the linker to add our dllmain.obj for __afxForceUSRDLL. So we need to define __afxForceUSRDLL in our own cpp file where our own DllMain is defined, then the linker will ignore mfc’s dllmodule.obj and see only one DllMain and never complains.

Source: http://social.msdn.microsoft.com/Forums/en-US/0d78aa6b-1e87-4c01-a4a7-691335b7351a/how-to-build-mfc-application-dll-in-visual-c-2010

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