Error 1 Error Lnk2005 Dllmain @12 Already Defined In Msvcrtd.libdllmain.obj
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on August 18, 2012 by Ofek Shilon We recently faced this linkage error: error LNK2005: _DllMain@12 already defined in MSVCRT.lib(dllmain.obj) Searching gives ~36K results as of July https://ofekshilon.com/2012/08/18/_dllmain12-already-defined/ 2012, many of which seem high quality (StackOverflow, MS, CodeProject etc.), and https://www.experts-exchange.com/questions/26267312/Visual-C-Compile-Error-error-LNK2005-DllMain-12-already-defined-in-DllMain-obj.html I was certain it would be a simple matter of finding a fix online and blindly applying it. However it seems the root cause in our particular case wasn’t covered yet (AFAIK), and it seems worthwhile to document. The MS KB article teaches that this is a linkage order error 1 problem – MFC libs must be linked before the CRT ones - but none of the fixes the article proposes worked. We did have one build configuration which was successful and one which failed with the above LNK2005 (Release – but it really doesn’t matter) so I dumped two /VERBOSE linker outputs for the two configurations and diffed them. After some admittedly error 1 error tedious inspection, an interesting difference came up – these lines were dumped only in the successful build: Found __afxForceUSRDLL … Referenced in Stdafx.obj Loaded mfcs100d.lib(dllmodul.obj) The symbol name implies that it is intended to force some linkage, and including it seems to have the beneficial effect of loading the mfc lib mfcs100d.lib. Indeed, searching reveals the following lines in dllmodul.cpp: #ifdef _X86_ extern "C" { int _afxForceUSRDLL; } #else extern "C" { int __afxForceUSRDLL; } #endif and the following in afx.h: // force inclusion of DLLMODUL.OBJ for _USRDLL #ifdef _USRDLL #pragma comment(linker, "/include:__afxForceUSRDLL") #endif So it turns out there’s a single condition that governs the linkage to the MFC library mfcs100/d (the one containing DllModul.obj, which exports _afxForceUSRDLL), and that condition is – _USRDLL being defined. Our linking project was indeed a dll and somehow the default _USRDLL preprocessor macro was missing from it – restoring the definition fixed the linkage. So bottom line, if you get a ‘DllMain@12 already defined’ linkage error for a dll, here’s another thing to try: make sure _USRDLL is defined in your project C++ property sheets. L
for Help Receive Real-Time Help Create a Freelance Project Hire for a Full Time Job Ways to Get Help Ask a Question Ask for Help Receive Real-Time Help Create a Freelance Project Hire for a Full Time Job Ways to Get Help Expand Search Submit Close Search Login Join Today Products BackProducts Gigs Live Careers Vendor Services Groups Website Testing Store Headlines Experts Exchange > Questions > Visual C++ Compile Error: error LNK2005: _DllMain@12 already defined in DllMain.obj Want to Advertise Here? Solved Visual C++ Compile Error: error LNK2005: _DllMain@12 already defined in DllMain.obj Posted on 2010-06-17 Editors IDEs Visual C++.NET System Programming 1 Verified Solution 5 Comments 3,532 Views Last Modified: 2013-12-14 I'm working on a DLL and now that I've included the MFC into my project I get the following error: mfcs100.lib(dllmodul.obj) : error LNK2005: _DllMain@12 already defined in DllMain.obj My understanding is that since I already have a DLLMain entry point in my DLL and the MFC has an entry point it creates a conflict. I can fix the issue by commenting out my DLLMain declaration but that's not desirable since I need to link to the process attach, thread attach, etc events. I've read several of the MSDN articles but wasn't able to get any suggestions to work. Does anyone know how to make MFC coexist in a DLL project? Thanks, Dan 0 Question by:dancablam Facebook Twitter LinkedIn Google LVL 33 Best Solution bypgnatyuk So the situation is easier then I thought about it. For you to know - you are supposed to use InitInstance. The DllMain exists, MFC provides it for you. If you insist, you will see here how to implement Go to Solution 5 Comments LVL 33 Overall: Level 33 Editors IDEs 13 System Programming 12 Visual C++.NET 12 Message Expert Comment by:pgnatyuk2010-06-17 The MFC dll has an own structure. The MFC Dlls (mainly the CRT library) should be linked in a special order. You can read and try the scenarios described here: http://support.microsoft.com/kb/148652 You can simply delete your version of DLLMain. I hope it will help. In case it does not, try the way I like and use all the time: You can create new MFC DLL project aside. Better with the same name. Then, copy your files into this new project. Or accurately copy the project settings and the main h and cpp files from this new project to he existing one. 0 LVL 3 Overall: Level 3 Message Author Comment by:dancablam2010-06-17 Deleting my DLLMain works but then how can I link in to the process attach